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

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 .

2017 AMC 10B Problem 2

Solution:

Problem 2 in Other Years