2017 AMC 10B Problem 2

Question

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?

5

minutes and

35

seconds

6

minutes and

40

seconds

7

minutes and

5

seconds

7

minutes and

25

seconds

8

minutes and

10

seconds

Find the time for the first

100

meters and the last

300

meters of one lap

Multiply one-lap time by

5

and convert seconds to minutes

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 .

Problem 2 in other years