A runner completes the first 10 laps of a 15-lap race at an average speed of 1 minute and thirty seconds per lap. How fast will the runner's average lap time need to be for the last five laps if they want to have average per-lap speed of one minute and twenty-five seconds for the entire race?

1 minute and five seconds

1 minute and eight seconds

1 minute and ten seconds

1 minute and fifteen seconds

1 minute and twenty seconds

Question

Mathematics

Guest

20 March, 10:41

A runner completes the first 10 laps of a 15-lap race at an average speed of 1 minute and thirty seconds per lap. How fast will the runner's average lap time need to be for the last five laps if they want to have average per-lap speed of one minute and twenty-five seconds for the entire race?

1 minute and five seconds

1 minute and eight seconds

1 minute and ten seconds

1 minute and fifteen seconds

1 minute and twenty seconds

+3

Answers (1)

Know the Answer?

Cindy James · Answer 1

The correct answer is 1 minute and 15 seconds.

To find this answer, we can write the equation below that combines the 2 rates. Then, solve for the missing variable.

10 (1.5) + 5 (x) = 15 (1 25/60)

15 + 5x = 21.25

5x = 6.25

x = 1.25

1.25 is one minute and a fourth of a minute. A fourth of a minute is 15 seconds.