A boat covers a certain distance upstream in 9 hours but takes 5 hours to return downstream to the starting place

A boat covers a certain distance upstream in 9 hours but takes 5 hours to return downstream to the starting place. If the speed of the boat in still water is 30 km/hr more than the speed of the stream, then find the distance covered by the boat in upstream?

a)            210 km

b)            180 km

c)            270 km

d)            150 km

e)            None of these

Sol:

Speed of the stream=x km/hr

Speed of the boat=(x+30) km/hr

Downstream distance=(x+30+x)*5 km

Upstream distance=(x+30-x)*9 km

(x+30+x)*5=(x+30-x)*9

(2x+30)*5=270

10x=270-150

x=12 km/hr

Speed of the boat=12+30=42 km/hr

Upstream distance=(12+30-12)*9=270 km