A boat covers 78 km downstream in 3 hours, while the time taken by a boat to go 182 km upstream and comes back to the same point

A boat covers 78 km downstream in 3 hours, while the time taken by a boat to go 182 km upstream and comes back to the same point is 20 hours, then find the ratio of the speed of the boat in still water to the speed of the stream.

a) 5: 2

b) 15: 4

c) 9: 4

d) 10: 3

e) 11: 5

Sol:

Downstream speed of boat = 78/3 = 26 km/h

According to the question:

Upstream speed = 14 km/h

Speed of boat in still water = (26 + 14)/2 = 20 km/h

Speed of stream = (26 – 14)/2 = 6 km/h

Required ratio = 20: 6 = 10: 3