A and B run a 1 km race A gives B a start of 50 m and still beats him by 15 seconds If A runs at 8 k...........

Quantitative Aptitude Time & distance

A and B run a 1 km race. A gives B a start of 50 m and still beats him by 15 seconds. If A runs at 8 km/h, what is the speed of B?

This questions was previously asked in

EPFO APFC (2015)

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Explanation:

Let a & b denote the running speeds (in m/s) of A & B respectively in a 1km (= 1000m) race.
It is mentioned that when A gives B a 50m start, A wins by 15 seconds. So we get the following equation,
Speed of A = 8km/hr = 8*1000/60*60 = 20/9 m/s

Time taken by A to finish the race = 1000/(20/9) = 450 second
Time taken by B to finish the race = 450 + 15 = 465 seconds.
So, speed of B = (1000 -50)/465
= 950/465 m/s
So, in km/hr (950/465) *(18/5) = 7.35km/hr ~ 7.4km/hr