2017 AMC 10B Problem 2

Problem 2 of 25EasierAlgebra

Sofia ran

5

laps around the

400

-meter track at her school. For each lap, she ran the first

100

meters at an average speed of

4

meters per second and the remaining

300

meters at an average speed of

5

meters per second. How much time did Sofia take running the

5

laps?

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Solution

She ran a total of

5\cdot 100=500

meters at

4

meters per second and

5\cdot 300=1500

meters at

5

meters per second. Therefore, her time is

\frac{500}4 + \frac{1500}5 = 425

seconds. This is equal to a total of

7

minutes and

5

seconds. Thus, the correct answer is C .