In a cross country race d km in length Marks average speed was 5m per s and Harrys average speed was 6m per s Harry finished 4 minutes ahead of Mark What was the length of the race?

Answer 1

s = d/t, where s is speed, d is distance, and t is time.
This can be rearranged to t = d/s
The time it took Mark to finish was d/5
The time it took Harry to finish was d/6
Harry finished 4*60 seconds (the time was given in minutes) ahead of mark, so:
d/5 = d/6 + 4*60

(THarry = TMark + 240 seconds)

d/5 = d/6 + 240

d/5 - d/6 = 240

6d/30 - 5d/30 = 240

d/30 = 240

d = 240*3

d = 7,200 meters