2. A man takes 3 hours 45 minutes to row a boat 15 km downstream of a river and 2 hours 30 minutes to cover a distance of 5 km upstream.Find the speed of the river current in km/hr?

4. There is a road beside a river.Two friends started from a place A moved to a temple situated at another place B and then returned to A again.One of them moves on a cycle at a speed of 12 km/hr while the other sails on a boat at a speed of 10 km/hr.If the river flows at the speed of 4 km/hr which of the two friends will return to place A first?

A. 7 km/hr B. 8 km/hr C. 8.4 km/hr D. 9.2 km/hr

Answer Answer: Option C Explanation: Clearly the cyclist moves both ways at a speed of 12 km/hr
so average speed of the cyclist = 12 km/hr
The boat sailor moves downstream at ( 10+4) i.e, 14 km/hr and upstream at (10-4) i.e, 6 km/hr
So average speed of the boat sailor =(2*14*6/14+6) km/hr = 42/5 km/hr = 8.4 km/hr
since the average speed of the cyclist is greater he will return to A first.

5. A man can row 7 1/2 km/ph in still water.If in a river running at 1.5 km an hour it takes him 50 minutes to row to place and back how far off is the place?

A. 4 km B. 5 km C. 6 km D. 3 km

Answer Answer: Option D Explanation: Speed downstream = (7.5+1.5) km/ph = 9 km/ph
Speed upstream = (7.5 - 1.5) km/hr = 6 km/ph
Let the required distance be X km.
x/9 +x/6 = 50/ 60 = 2x+3x =( 5/6*18) = 5x = 15 = x= 3 km.