Question

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?​

Answer 1

Given :-

• Average speed for first 10 laps = 1 minute, 30 seconds / Lap.
• Total average speed need for the entire race = 1 minutes , 25 seconds / Lap.

To Find :-

• Average lap time for the last 5 laps . ?

Solution :-

we have given that,

→ Average speed for first 10 laps = 1 minute, 30 seconds / Lap. = 60 seconds + 30 seconds = 90 seconds / Lap.

So,

→ Total time taken to cover first 10 laps = 10 * 90 = 900 seconds.

Now, we have given that,

→ Total average speed need for the entire race = 1 minutes , 25 seconds / Lap. = 60 seconds + 25 seconds = 85 seconds / Lap.

So,

→ Total time taken to cover complete race = 15 * 85 = 1275 seconds.

Therefore,

→ Total Time taken to cover last 5 steps = Total time of race - Total time of first 10 Laps = 1275 - 900 = 375 seconds.

Hence,

→ Average lap time for the last 5 laps = (Total Time) / (Number of Laps)

→ Average Lap time = (375/5) = 75 seconds . = 1 minute , 15 seconds. (Ans.)

Hence, Average lap time for the last 5 laps is 1 minute, 15 seconds .

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