The upstream speed of a boat is 9 km/hr which is 300% more than the speed of stream . Find how much distance boat will cover in 5 hours while travelli

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The upstream speed of a boat is 9 km/hr which is 300% more than the speed of stream . Find how much distance boat will cover in 5 hours while travelling in downstream .
A. 66 km
B. 65.5 km
C. 67.5 km
D. 68 km

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Let the speed of stream be x km/hr
Then ,
Speed of boat in upstream =  x xx (400)/(100) = 9
implies x = 2.25 km/hr
Speed of boat in still water = 9 + 2.25 = 11.25 km/hr
Distance covered in 3 hours in downstream
= (11.25 + 2.25) xx 5 = 67.5 km