A taxi ride costs 0.25 per mile traveled. How much does a 5-mile taxi ride cost?
- A)
- B)
- C)
- D)
- E)
Answer
C
Key insight
The 1.50 is paid once, but the 0.25 is paid again for every mile, so add 1.50 to 5 times 0.25.
Solution
The price has two parts, so work them out one at a time.
1. The part you always pay. Getting in the taxi costs , no matter how far you go.
2. The part that grows with distance. Every mile adds . For miles that is
3. Add the two parts.
A quick check: is a quarter, and quarters is , which matches Step 2.
The ride costs .
Why this works
Many word problems have the shape "a fixed amount plus so much for each unit": taxi fares, phone plans, bike rentals. Find the number that is paid once and the number that gets multiplied by the quantity. Then multiply and add. A cost of is an example of a linear formula, and this problem only asks you to put in miles.
The trap
Adding 0.25 only once (getting 1.75) instead of paying it for each of the 5 miles.
Concise solution
The ride has two parts: a flat charge of that is paid regardless of distance, and a distance charge of for every mile.
Five miles cost dollars. Adding the flat charge:
The ride costs .
Review in the AoPS books
- Introduction to Algebra, Chapter 3: One-Variable Linear Equations (§3.3, §3.4)
- Introduction to Algebra, Chapter 7: Proportion (§7.4)
Techniques
Set up the equation/formula and compute; no special trick needed