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A and B cycle along a circular track from the same point and at the same time, but in the opposite direction.
It takes A 30 minutes to complete one round. How long does it take B to complete one round if they meet 21 minutes later?
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Let L be the length of the circular track (in any length unit, for example, in meters))
and let x be the time for B to complete one round, in minutes (the unknown value under the problem's question).
Then the rate of moving for A is meters per minute;
the rate of moving for B is meters per minute.
The total distance traveled by both cyclists in 21 minutes (till the meeting moment) is the track length L.
It gives you THIS total traveled distance equation
{ = L.
Cancel L in both sides
+ = 1.
It implies
= 1 - = = =
Hence,
x = = 7*10 = 70.
ANSWER. It requires 70 minutes for B to complete one round.
Solved.
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It is a nice Travel @ Distance problem.
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