Topics / Algebra
Linear Equations & Word Problems
Linear equations/inequalities, word problems, rates, work, mixtures, distance-speed-time
What you need to know
- A linear equation in one unknown has exactly one solution, unless it collapses to or .
- Distance rate time; work done rate time. Finishing a job alone in hours means a rate of job per hour, and rates of workers or pipes add.
- Average speed is total distance over total time, never the average of the speeds.
- Mixtures: pure substance is conserved, so . Ages: the difference between two ages never changes.
How AMC 10 tests it
- Problems 1–8: a short word problem (ages, coins, a two-part trip) that becomes one equation .
- Problems 5–12: work or pipe problems where the intended idea is to add rates, not times.
- Round-trip speed problems where the mean of the two speeds is a listed wrong choice.
- Problems asking for something other than the natural unknown: , the other person's age, a percent.
Standard approaches
- Name the unknown you are asked for and translate each sentence into one equation.
- Convert everything to a rate per unit time; for trips, set the distance to or a convenient common multiple.
- Pick a friendly total (LCM of the times, for percents) to avoid fractions.
- If the equation is messy, test the answer choices against the story.
Worked example
A pump fills an empty tank in hours, and a drain empties a full tank in hours. The tank starts empty with the pump running and the drain closed. After hours the drain is opened, and the tank becomes exactly full hours after that. What is ?
(A) (B) (C) (D) (E)
Take the tank as unit. The pump adds per hour and the drain removes , so with both open the net rate is . The pump alone fills in the first hours; the next hours add . Thus
The answer is .
Pitfalls
- Averaging the two speeds instead of dividing total distance by total time.
- Adding times instead of rates ("alone and hours, so together ").
- Solving for but answering a different quantity than the one asked.
- Dropping a unit conversion (minutes versus hours).
Traps that recur
- Assuming that once Michael catches the truck he stays ahead, or missing the two meetings where the gap only touches zero at the end of a stop or a drive. (2008 AMC 10B #25)
- Forgetting to subtract the lunch break from every day's working time, or converting 2:12 PM and 7:12 PM to hours incorrectly (372 and 672 minutes after 8:00). (2012 AMC 10A #19)
- Comparing the second mean to the original mean instead of to the enlarged list's mean (it should be m + 2 - 1 = m + 1 with n + 2 numbers). (2002 AMC 10B #25)
- Writing c + m = 8p and m/4 + c/6 = 8, then stalling with two equations in three unknowns instead of using that c and m are positive. (2000 AMC 10 #22)
Problems, easiest first
Andy and Betsy both live in Mathville. Andy leaves Mathville on his bicycle at , traveling due north at a steady miles per hour. Betsy leaves on her bicycle from the same point at , traveling due east at a steady miles per hour. At what time will they be exactly the same distance from their …
A model used to estimate the time it will take to hike to the top of the mountain on a trail is of the form where and are constants, is the time in minutes, is the length of the trail in miles, and is the altitude gain in feet. The model estimates that it will take minutes to hike to …
Maddy and Lara see a list of numbers written on a blackboard. Maddy adds to each number in the list and finds that the sum of her new numbers is . Lara multiplies each number in the list by and finds that the sum of her new numbers is also . How many numbers are written on the blackboard?
Cities and are miles apart. Alicia lives in and Beth lives in . Alicia bikes towards at miles per hour. Leaving at the same time, Beth bikes toward at miles per hour. How many miles from City will they be when they meet?
The weight of of a large pizza together with cups of orange slices is the same weight of of a large pizza together with cups of orange slices. A cup of orange slices weigh of a pound. What is the weight, in pounds, of a large pizza?
The sum of three numbers is The first number is times the third number, and the third number is less than the second number. What is the absolute value of the difference between the first and second numbers?
Mr. Lopez has a choice of two routes to get to work. Route A is miles long, and his average speed along this route is miles per hour. Route B is miles long, and his average speed along this route is miles per hour, except for a -mile stretch in a school zone where his average speed is …
Portia's high school has times as many students as Lara's high school. The two high schools have a total of students. How many students does Portia's high school have?
Menkara has a index card. If she shortens the length of one side of this card by inch, the card would have area square inches. What would the area of the card be in square inches if instead she shortens the length of the other side by inch?
At a math contest, students are wearing blue shirts, and another students are wearing yellow shirts. The students are assigned into pairs. In exactly of these pairs, both students are wearing blue shirts. In how many pairs are both students wearing yellow shirts?
A driver travels for hours at miles per hour, during which her car gets miles per gallon of gasoline. She is paid per mile, and her only expense is gasoline at per gallon. What is her net rate of pay, in dollars per hour, after this expense?
What value of satisfies
Ana and Bonita are born on the same date in different years, years apart. Last year Ana was times as old as Bonita. This year Ana's age is the square of Bonita's age. What is
Sam drove miles in minutes. His average speed during the first minutes was mph (miles per hour), and his average speed during the second minutes was mph. What was his average speed, in mph, during the last minutes?
Sofia ran laps around the -meter track at her school. For each lap, she ran the first meters at an average speed of meters per second and the remaining meters at an average speed of meters per second. How much time did Sofia take running the laps?
Camilla had twice as many blueberry jelly beans as cherry jelly beans. After eating pieces of each kind, she now has three times as many blueberry jelly beans as cherry jelly beans. How many blueberry jelly beans did she originally have?
Pablo buys popsicles for his friends. The store sells single popsicles for each, -popsicle boxes for each, and -popsicle boxes for . What is the greatest number of popsicles that Pablo can buy with ?
The sum of two positive numbers is times their difference. What is the ratio of the larger number to the smaller number?
A box contains a collection of triangular and square tiles. There are tiles in the box, containing edges total. How many square tiles are there in the box?
Isaac has written down one integer two times and another integer three times. The sum of the five numbers is , and one of the numbers is What is the other number?
Roy's cat eats of a can of cat food every morning and of a can of cat food every evening. Before feeding his cat on Monday morning, Roy opened a box containing cans of cat food. On what day of the week did the cat finish eating all the cat food in the box?
Bridget bakes 48 loaves of bread for her bakery. She sells half of them in the morning for each. In the afternoon she sells two thirds of what she has left, and because they are not fresh, she charges only half price. In the late afternoon she sells the remaining loaves at a dollar each. Each loaf …
Leah has coins, all of which are pennies and nickels. If she had one more nickel than she has now, then she would have the same number of pennies as nickels. In cents, how much are Leah's coins worth?
Susie pays for muffins and bananas. Calvin spends twice as much paying for muffins and bananas. A muffin is how many times as expensive as a banana?
Tom, Dorothy, and Sammy went on a vacation and agreed to split the costs evenly. During their trip Tom paid , Dorothy paid , and Sammy paid . In order to share costs equally, Tom gave Sammy dollars, and Dorothy gave Sammy dollars. What is ?
On a particular January day, the high temperature in Lincoln, Nebraska, was degrees higher than the low temperature, and the average of the high and the low temperatures was . In degrees, what was the low temperature in Lincoln that day?
A taxi ride costs 0.25 per mile traveled. How much does a 5-mile taxi ride cost?
For a science project, Sammy observed a chipmunk and a squirrel stashing acorns in holes. The chipmunk hid 3 acorns in each of the holes it dug. The squirrel hid 4 acorns in each of the holes it dug. They each hid the same number of acorns, although the squirrel needed 4 fewer holes. How many acorns did the chipmunk …
Cagney can frost a cupcake every seconds and Lacey can frost a cupcake every seconds. Working together, how many cupcakes can they frost in minutes?
Last year adult cats, half of whom were female, were brought into the Smallville Animal Shelter. Half of the adult female cats were accompanied by a litter of kittens. The average number of kittens per litter was . What was the total number of cats and kittens received by the shelter last year?
Each third-grade classroom at Pearl Creek Elementary has 18 students and 2 rabbits. How many more students than rabbits are there in all 4 of the third-grade classrooms?
LeRoy and Bernardo went on a week-long trip together and agreed to share the costs equally. Over the week, each of them paid for various joint expenses such as gasoline and car rental. At the end of the trip, it turned out that LeRoy had paid dollars and Bernardo had paid dollars, where . How many …
A cell phone plan costs each month, plus ¢ per text message sent, plus ¢ for each minute used over hours. In January Michelle sent text messages and talked for hours. How much did she have to pay?
Tyrone had marbles and Eric had marbles. Tyrone then gave some of his marbles to Eric so that Tyrone ended with twice as many marbles as Eric. How many marbles did Tyrone give to Eric?
A book that is to be recorded onto compact discs takes minutes to read aloud. Each disc can hold up to minutes of reading. Assume that the smallest possible number of discs is used and that each disc contains the same length of reading. How many minutes of reading will each disc contain?
Eric plans to compete in a triathlon. He can average miles per hour in the -mile swim and miles per hour in the -mile run. His goal is to finish the triathlon in hours. To accomplish his goal what must his average speed in miles per hour, be for the -mile bicycle ride?
One can holds ounces of soda, what is the minimum number of cans needed to provide a gallon ( ounces) of soda?
Each morning of her five-day workweek, Jane bought either a -cent muffin or a -cent bagel. Her total cost for the week was a whole number of dollars. How many bagels did she buy?
A semipro baseball league has teams with players each. League rules state that a player must be paid at least and that the total of all players' salaries for each team cannot exceed What is the maximum possible salary, in dollars, for a single player?
The larger of two consecutive odd integers is three times the smaller. What is their sum?
Doug and Dave shared a pizza with equally-sized slices. Doug wanted a plain pizza, but Dave wanted anchovies on half the pizza. The cost of a plain pizza was dollars, and there was an additional cost of dollars for putting anchovies on one half. Dave ate all the slices of anchovy pizza and one plain slice. …
Sandwiches at Joe's Fast Food cost each and sodas cost each. How many dollars will it cost to purchase sandwiches and sodas?
A football game was played between two teams, the Cougars and the Panthers. The two teams scored a total of points, and the Cougars won by a margin of points. How many points did the Panthers score?
The equations and have the same solution . What is the value of ?
A store normally sells windows at each. This week the store is offering one free window for each purchase of four. Dave needs seven windows and Doug needs eight windows. How many dollars will they save if they purchase the windows together rather than separately?
You and five friends need to raise dollars in donations for a charity, dividing the fundraising equally. How many dollars will each of you need to raise?
It takes Anna minutes to walk uphill km from her home to school, but it takes her only minutes to walk from school to her home along the same route. What is her average speed, in km/hr, for the round trip?
Al gets the disease algebritis and must take one green pill and one pink pill each day for two weeks. A green pill costs $1\ for the two weeks. How much does one green pill cost?
Members of the Rockham Soccer League buy socks and T-shirts. Socks cost 5 more than a pair of socks. Each member needs one pair of socks and a shirt for home games and another pair of socks and a shirt for away games. If the total cost is $2366, how many members are in the League?
Cindy was asked by her teacher to subtract 3 from a certain number and then divide the result by 9. Instead, she subtracted 9 and then divided the result by 3, giving an answer of 43. What would her answer have been had she worked the problem correctly?
The sum of two numbers is . Suppose is added to each number and then each of the resulting numbers is doubled. What is the sum of the final two numbers?
A number is more than the product of its reciprocal and its additive inverse. In which interval does the number lie?
Chandra pays an on-line service provider a fixed monthly fee plus an hourly charge for connect time. Her December bill was , but in January her bill was because she used twice as much connect time as in December. What is the fixed monthly fee?
Amy, Bomani, Charlie, and Daria work in a chocolate factory. On Monday Amy, Bomani, and Charlie started working at and were able to pack , , and packages, respectively, every minutes. At some later time, Daria joined the group, and Daria was able to pack packages every minutes. …
Barb the baker has developed a new temperature scale for her bakery called the Breadus scale, which is a linear function of the Fahrenheit scale. Bread rises at degrees Fahrenheit, which is degrees on the Breadus scale. Bread is baked at degrees Fahrenheit, which is degrees on the Breadus scale. …
At noon on a certain day, Minneapolis is degrees warmer than St. Louis. At the temperature in Minneapolis has fallen by degrees while the temperature in St. Louis has risen by degrees, at which time the temperatures in the two cities differ by degrees. What is the product of all possible values …
Chantal and Jean start hiking from a trailhead toward a fire tower. Jean is wearing a heavy backpack and walks slower. Chantal starts walking at miles per hour. Halfway to the tower, the trail becomes really steep, and Chantal slows down to miles per hour. After reaching the tower, she immediately turns around …
Elmer the emu takes equal strides to walk between consecutive telephone poles on a rural road. Oscar the ostrich can cover the same distance in equal leaps. The telephone poles are evenly spaced, and the st pole along this road is exactly one mile ( feet) from the first pole. How much longer, in …
Joe has a collection of coins, consisting of -cent coins, -cent coins, and -cent coins. He has more -cent coins than -cent coins, and the total value of his collection is cents. How many more -cent coins does Joe have than -cent coins?
Samia set off on her bicycle to visit her friend, traveling at an average speed of kilometers per hour. When she had gone half the distance to her friend's house, a tire went flat, and she walked the rest of the way at kilometers per hour. In all it took her minutes to reach her friend's house. In …
Minnie rides on a flat road at kilometers per hour (kph), downhill at kph, and uphill at kph. Penny rides on a flat road at kph, downhill at kph, and uphill at kph. Minnie goes from town to town , a distance of km all uphill, then from town to town , a distance of …
Trickster Rabbit agrees with Foolish Fox to double Fox's money every time Fox crosses the bridge by Rabbit's house, as long as Fox pays coins in toll to Rabbit after each crossing. The payment is made after the doubling, Fox is excited about his good fortune until he discovers that all his money is gone after …
At Megapolis Hospital one year, multiple-birth statistics were as follows: Sets of twins, triplets, and quadruplets accounted for of the babies born. There were four times as many sets of triplets as sets of quadruplets, and there was three times as many sets of twins as sets of triplets. How many of these …
The ratio of the measures of two acute angles is , and the complement of one of these two angles is twice as large as the complement of the other. What is the sum of the degree measures of the two angles?
Sola decided to fence in his rectangular garden. He bought fence posts, placed one on each of the four corners, and spaced out the rest evenly along the edges of the garden, leaving exactly yards between neighboring posts. The longer side of his garden, including the corners, has twice as many posts as the …
Two years ago Pete was three times as old as his cousin Claire. 2 years before that, Pete was four times as old as Claire. In how many years will the ratio of their ages be : ?
Camden constructs a square window using equal-size panes of glass, as shown. The ratio of the height to width for each pane is , and the borders around and between the panes are inches wide. In inches, what is the side length of the square window?
A truck travels feet every seconds. There are feet in a yard. How many yards does the truck travel in minutes?
A basketball team's players were successful on 50% of their two-point shots and 40% of their three-point shots, which resulted in 54 points. They attempted 50% more two-point shots than three-point shots. How many three-point shots did they attempt?
A softball team played ten games, scoring 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 runs. They lost by one run in exactly five games. In each of their other games, they scored twice as many runs as their opponent. How many total runs did their opponents score?
It takes Clea 60 seconds to walk down an escalator when it is not operating, and only 24 seconds to walk down the escalator when it is operating. How many seconds does it take Clea to ride down the operating escalator when she just stands on it?
The players on a basketball team made some three-point shots, some two-point shots, and some one-point free throws. They scored as many points with two-point shots as with three-point shots. Their number of successful free throws was one more than their number of successful two-point shots. The team's total score was …
On Halloween Casper ate of his candies and then gave candies to his brother. The next day he ate of his remaining candies and then gave candies to his sister. On the third day he ate his final candies. How many candies did Casper have at the beginning?
The average of the numbers and is . What is ?
Tony works hours a day and is paid 0.5050 . How old was Tony at the end of the six month period?
Shelby drives her scooter at a speed of miles per hour if it is not raining, and miles per hour if it is raining. Today she drove in the sun in the morning and in the rain in the evening, for a total of miles in minutes. How many minutes did she drive in the rain?
Angelina drove at an average rate of km/h and then stopped minutes for gas. After the stop, she drove at an average rate of km/h. Altogether she drove km in a total trip time of hours including the stop. Which equation could be used to solve for the time in hours that she drove before her …
When a bucket is two-thirds full of water, the bucket and water weigh kilograms. When the bucket is one-half full of water the total weight is kilograms. In terms of and , what is the total weight in kilograms when the bucket is full of water?
Doug can paint a room in hours. Dave can paint the same room in hours. Doug and Dave paint the room together and take a one-hour break for lunch. Let be the total time, in hours, required for them to complete the job working together, including lunch. Which of the following equations is satisfied by ?
While Steve and LeRoy are fishing 1 mile from shore, their boat springs a leak, and water comes in at a constant rate of 10 gallons per minute. The boat will sink if it takes in more than 30 gallons of water. Steve starts rowing toward the shore at a constant rate of 4 miles per hour while LeRoy bails water out of the …
The will be scored by awarding points for each correct response, points for each incorrect response, and points for each problem left unanswered. After looking over the problems, Sarah has decided to attempt the first and leave only the last unanswered. How many of the …
Tom's age is years, which is also the sum of the ages of his three children. His age years ago was twice the sum of their ages then. What is ?
Josh and Mike live miles apart. Yesterday Josh started to ride his bicycle toward Mike's house. A little later Mike started to ride his bicycle toward Josh's house. When they met, Josh had ridden for twice the length of time as Mike and at four-fifths of Mike's rate. How many miles had Mike ridden when they met?
Bertha has 6 daughters and no sons. Some of her daughters have 6 daughters, and the rest have none. Bertha has a total of 30 daughters and granddaughters, and no great-granddaughters. How many of Bertha's daughters and grand-daughters have no daughters?
Patty has coins consisting of nickels and dimes. If her nickels were dimes and her dimes were nickels, she would have cents more. How much are her coins worth?
Al, Betty, and Clare split among them to be invested in different ways. Each begins with a different amount. At the end of one year, they have a total of dollars. Betty and Clare have both doubled their money, whereas Al has managed to lose dollars. What was Al's …
Moe uses a mower to cut his rectangular -foot by -foot lawn. The swath he cuts is inches wide, but he overlaps each cut by inches to make sure that no grass is missed. He walks at the rate of feet per hour while pushing the mower. Which of the following is closest to the number of hours it …
For which of the following values of does the equation have no solution for ?
Mr. Earl E. Bird gets up every day at 8:00 AM to go to work. If he drives at an average speed of 40 miles per hour, he will be late by 3 minutes. If he drives at an average speed of 60 miles per hour, he will be early by 3 minutes. How many miles per hour does Mr. Bird need to drive to get to work exactly on time?
Emily sees a ship traveling at a constant speed along a straight section of a river. She walks parallel to the riverbank at a uniform rate faster than the ship. She counts equal steps walking from the back of the ship to the front. Walking in the opposite direction, she counts steps of the same size from the …
David drives from his home to the airport to catch a flight. He drives miles in the first hour, but realizes that he will be hour late if he continues at this speed. He increases his speed by miles per hour for the rest of the way to the airport and arrives minutes early. How many miles is the …
Three runners start running simultaneously from the same point on a -meter circular track. They each run clockwise around the course maintaining constant speeds of , , and meters per second. The runners stop once they are all together again somewhere on the circular course. How many seconds do …
Roy bought a new battery-gasoline hybrid car. On a trip the car ran exclusively on its battery for the first 40 miles, then ran exclusively on gasoline for the rest of the trip, using gasoline at a rate of 0.02 gallons per mile. On the whole trip he averaged 55 miles per gallon. How long was the trip in miles?
A shopper plans to purchase an item that has a listed price greater than and can use any one of the three coupons. Coupon A gives off the listed price, Coupon B gives off the listed price, and Coupon C gives off the amount by which the listed price exceeds …
On a -question multiple choice math contest, students receive points for a correct answer, points for an answer left blank, and point for an incorrect answer. Jesse’s total score on the contest was . What is the maximum number of questions that Jesse could have answered correctly?
Andrea and Lauren are kilometers apart. They bike toward one another with Andrea traveling three times as fast as Lauren, and the distance between them decreasing at a rate of kilometer per minute. After minutes, Andrea stops biking because of a flat tire and waits for Lauren. After how many minutes from …
Yesterday Han drove 1 hour longer than Ian at an average speed 5 miles per hour faster than Ian. Jan drove 2 hours longer than Ian at an average speed 10 miles per hour faster than Ian. Han drove 70 miles more than Ian. How many more miles did Jan drive than Ian?
Bricklayer Brenda would take nine hours to build a chimney alone, and Bricklayer Brandon would take hours to build it alone. When they work together, they talk a lot, and their combined output decreases by bricks per hour. Working together, they build the chimney in hours. How many bricks are in the …
Yan is somewhere between his home and the stadium. To get to the stadium he can walk directly to the stadium, or else he can walk home and then ride his bicycle to the stadium. He rides 7 times as fast as he walks, and both choices require the same amount of time. What is the ratio of Yan's distance from his home to …
Odell and Kershaw run for minutes on a circular track. Odell runs clockwise at and uses the inner lane with a radius of meters. Kershaw runs counterclockwise at and uses the outer lane with a radius of meters, starting on the same radial line as Odell. How many times …
Brenda and Sally run in opposite directions on a circular track, starting at diametrically opposite points. They first meet after Brenda has run 100 meters. They next meet after Sally has run 150 meters past their first meeting point. Each girl runs at a constant speed. What is the length of the track in meters?
Paula the painter and her two helpers each paint at constant, but different, rates. They always start at AM, and all three always take the same amount of time to eat lunch. On Monday the three of them painted 50% of a house, quitting at PM. On Tuesday, when Paula wasn't there, the two helpers painted only …
When is appended to a list of integers, the mean is increased by . When is appended to the enlarged list, the mean of the enlarged list is decreased by . How many integers were in the original list?
One morning each member of Angela's family drank an 8-ounce mixture of coffee with milk. The amounts of coffee and milk varied from cup to cup, but were never zero. Angela drank a quarter of the total amount of milk and a sixth of the total amount of coffee. How many people are in the family?
Michael walks at the rate of feet per second on a long straight path. Trash pails are located every feet along the path. A garbage truck travels at feet per second in the same direction as Michael and stops for seconds at each pail. As Michael passes a pail, he notices the truck ahead of him just …