AMC 10 Step by Step

2026 AMC 10A

All 25 problems, 75 minutes, scored 6 / 1.5 / 0. The answer key and the idea behind each problem are on this page too, folded away until you ask for them.

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The problems

Show the answer key, topics and key insights

This gives away all 25 answers and the idea behind each one. Sit the paper first if you mean to.

The same key as a PDF 133 KB — a separate file from the paper, so one can be handed over without the other.

#AnswerTopicDifficultyKey insight
1BRatios, Percents & AveragesMeasure every record in EP-lengths. One LP counts as 3 EPs, so the 33 LPs play as long as 99 EPs.
2ARatios, Percents & AveragesThe 27 percent is figured on the price before tax. The customer pays 127 percent of that price, so the tax is 27 parts out of 127.
3DTriangles: Area & PythagoreanBase BE is 12 and lies on the bottom side, so only the height of F matters. The two lines cross 8 units above the bottom.
4AAngles & PolygonsA 150 and a 190 average out to 170 degrees, so the angle sum is 170 per side. Setting that equal to 180 times (sides minus 2) gives 36 sides.
5CSequences & SeriesAdding a new number equal to the current average leaves the average unchanged. So once the third term is 142, every later term is 142 too.
6ACircles16-30-34 is a right triangle, so its longest side is a diameter. That diameter splits the circle into two halves, and the triangle sits inside one half.
7ASystems of EquationsSubtracting the equations removes x and leaves y + z = 5. Then x must be 26, and only the pairs of positive whole numbers adding to 5 remain.
8CLinear Equations & Word ProblemsTo make the needed speed as small as possible, take the shortest distance that rounds to 7 miles and the longest time that rounds to 5 minutes.
9DSimilar & Congruent TrianglesEnlarging makes every side longer, so the big triangle's 9 must come from the small triangle's third side, and its 12 from the small triangle's 9.
10CStatistics & DataUse the sum-of-squares formula for the mean and the middle square for the median, both in terms of n, then make the mean 1.32 times the median.
11DGCD & LCMThe least common multiple of 2, 5, 24, 60 and 240 is 240. So either n is a multiple of 240, or n is a divisor of 240.
12DBasic ProbabilityPicture the socks in a random line. The socks left over are the unbroken same-color run at the end, so read the line from the back.
13CBasic CountingWithin-club plus between-club handshakes is all handshakes: 231, so 22 people. Between-club handshakes are the product of the two club sizes.
14BTriangles: Area & PythagoreanWrite all three triangle inequalities. Each becomes a quadratic inequality in t that factors, and together they trap t strictly between 2 and 10.
15BGames & ProcessesWork upward. The node 20/27 has a partner 7/27 (they add to 1), and their parent is 7/20. Repeat until you reach 1/2, counting the steps.
16DBasic ProbabilityBalls beyond a color's cap score nothing. Waste as many as possible: the lowest score, 4, needs either no reds or all six reds.
17CQuadrilaterals & Polygon AreasEach square reaches 1 unit inward, but the center is only √3/2 inward, so the small hexagon's center-to-side distance is 1 − √3/2.
18DSequences & SeriesMeasure every term by how far it sits above 4. That distance is cut in half at each step, and it must stay a whole number through ten halvings.
19CSolid GeometryThe cover's center sits on the table and the top corners are hardest to reach. Find the smallest circle around the footprint, then add the height 2 by Pythagoras.
20CDistributions & Stars and Bars510,510 is the product of the seven primes 2 through 17, each used once. A box is just a way to split these seven primes into three non-empty groups.
21CPaths & GridsTwo scoring sections need all four X's, two in each, so the third section is all O's. Only two all-O sections exist; count the partitions around each.
22ACoordinate GeometryHalf a turn about the point halfway between two centers swaps those two equal ellipses, so if they touch, they touch exactly at that halfway point.
23DNumber PropertiesEvery 6 consecutive integers hold exactly 3 even numbers and 2 multiples of 3, so only the leftover 0 to 5 numbers decide which pairs appear.
24DPolynomialsSubtract the two values. The constant cancels, and what remains depends only on the inputs' sum 6 and product 4, forcing c = −32 − 6b.
25BGames & ProcessesRoom 1 gains at most one nut a day while the average gains 0.9, so it catches up only 0.1 a day; starting 9.5 behind takes 95 days.