The rate of current is 5km/hr and the speed of boat in still water is 19km/hr. The ratio between the distance travelled downstream in 15 minutes to the distance travelled upstream in 30 minutes is:
If the speed of boat in still water is u km/hr and the speed of the stream is v km/hr, then:
Speed downstream = (u + v) km/hr.
Speed upstream = (u - v) km/hr.
Given that the speed of boat in still water is 19 km/hr and the rate of current is 5 km/hr.
Downstream speed = (19 + 5) km/hr = 24km/hr
Distance travelled downstream in 15 minutes with a speed of 24km/hr = 24 x (15/60) = 6 km
Upstream speed = (19 - 5) km/hr = 14km/hr
Distance travelled upstream in 30 minutes with a speed of 14km/hr = 14 x(30/60) = 7 km
Then the required ratio = 6:7 = 3 : 3.5
Hence the answer is 3 : 3.5
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