A boat can travel 12.8 km downstream in 32 min. If the speed of the water current is 1/5th of the speed of the boat in still water, what distance (in km) the boat can travel upstream in 135 min ?
Let speed of boat in still water = $$5x$$ km/min
=> Speed of water current = $$x$$ km/min
=> Downstream speed = $$(5x + x) = 6x$$ km/min
Acc. to ques, => $$6x = \frac{12.8}{32}$$
=> $$x = \frac{0.4}{6} = \frac{1}{15}$$
=> Upstream speed = $$(5x - x) = 4x = \frac{4}{15}$$ km/min
$$\therefore$$ Distance covered by boat in 135 min = $$\frac{4}{15} \times 135$$
= $$4 \times 9 = 36$$ km
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