Question

A boat moving downstream 28 km in 4 hours and upstream 20 km in 5 hours. Find the ratio between the speed of the stream and speed of a boat in still water

• A. 3 : 11
• B. 11 : 13
• C. 8 : 3
• D. 8 : 11

Answer 1

Answer:

A. 3 : 11

If speed of stream = y km/hour and speed of boat = x km/hour Downstream speed = (x + y) km/hour Upstream speed = (x – y) km/hour Speed downstream: (x + y) = 28/4 = 7 km/hour Speed upstream: (x – y) = 20/5 = 4 km/hour Speed of the stream = ½ × (7 - 4) = 1.5 km/hour Speed of boat in still water = ½ × (7 + 4) = 5.5 km/hour Required ratio = 1.5 : 5.5 = 3 : 11