Q. 5:John jogs on track A at 6 kmph and Mary jogs on track B at 7.5 kmph. The total length of tracks A and B is 325 metres. While John makes 9 rounds of track A, Mary makes 5 rounds of track B. In how many seconds will Mary make one round of track A?
Since distance = speed * time, so
Let length of track a be a and that of b be 325-a
9a/6 = 5(325-a)/7.5 (same time)
67.5a = 9750-30a
A = 100 and B = 225 metres
Time taken by mary = 100/7.5*5/18 = 48 sec