A and B take part in a 100 metres race. A runs at 5 km an hour. A gives B a start of 8 metres and still beats him by 8 seconds. The speed of B is ?

A's speed = 5 km/hr
= $$\left( {5 \times \frac{5}{{18}}} \right)$$  m/sec
= $$\frac{25}{18}$$ m/sec
Time taken by A to cover 100 metres
= $$\left( {100 \times \frac{{18}}{{25}}} \right)$$
= 72 sec
Time taken by B to cover 92 metres
= (72 + 8) sec
= 80 sec
B's speed
$$\frac{92}{80}$$ m/sec
= $$\left( {\frac{{92}}{{80}} \times \frac{{18}}{5}} \right)$$  km/hr
= $$\frac{414}{100}$$ km/hr
= 4.14 km/hr