Downstream speed of the boat is 5 km/hr more than the speed of the boat in still water and the time taken by the boat to cover 200 km

Downstream speed of the boat is 5 km/hr more than the speed of the boat in still water and the time taken by the boat to cover 200 km in downstream is equal to the time taken by the boat to cover 120 km in upstream. Find the distance covered by the boat in still water in 6 hours.

a)            240 km

b)            200 km

c)            120 km

d)            180 km

e)            None of these

Sol:

Let the speed of the boat in still water be B km/hr

and the speed of the current be C km/hr.

B + C = 5 + B

C = 5 km/hr

200/(B + 5) = 120/(B – 5)

5/(B + 5) = 3/(B – 5)

5B – 25 = 3B + 15

2B = 40

B = 20 km/hr

Required distance = 20 * 6 = 120 km