The ratio between the speed of the boat in upstream and the speed of the stream are 6:5 respectively. The boat can cover (d+140) km distance in downstream in 28 hours. The same boat can cover (d+100) km in still water in 40 hours. Find out the time taken by the same boat to cover (d-240) km distance in upstream.
The ratio between the speed of the boat in upstream and the speed of the stream are 6:5 respectively.
Let’s assume the speed of the boat in upstream and the speed of the stream are ‘6a‘ and ‘5a‘ respectively.
Speed of boat in downstream = 6a+5a+5a = 16a
Speed of boat in still water = 16a-5a = 11a
The boat can cover (d+140) km distance in downstream in 28 hours.
(d+140)/28 = 16a
(d+140) = 448a
d = 448a-140Â Â Eq.(i)
The same boat can cover (d+100) km in still water in 40 hours.
(d+100)/40 = 11a
(d+100) = 440a
d = 440a-100Â Â Eq.(ii)
So Eq.(i) = Eq.(ii)
448a-140 = 440a-100
448a-440a = 140-100
8a = 40
a = 5
Put the value of ‘a’ in Eq.(i).
d = 448x5-140
= 2240-140
= 2100
Time taken by the same boat to cover (d-240) km distance in upstream = (d-240)/(6a)
Put the value of ‘d’ and ‘a’ in the above equation.
= (2100-240)/(6x5)
= 1860/30
= 62 hours
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