Question

pratik takes 8 hours to travel 36 km downstream and return to the same spot . the speed of boat in steel water is 12 km per hour . Find the speed of water current.

Answer 1

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Ans-----> Let speed of water current is x km/h
speed of boat in still water = 12 km/h
Distance = 36 km
Downstream speed = (12 + x) km/h
Upstream speed = (12 - x) km/h

A/C to question,
Total time taken by Pratik = 8 hrs
time taken to travel 36 km downstream + time
taken to travel 36 km Upstream = 8hrs
⇒36/(12 + x) + 36/(12 - x) = 8
⇒ 36 [ 1/(12 + x ) + 1/(12 - x) ] = 8
⇒ 9[ {(12 - x) + (12 + x)}/(12² - x²) ] = 2
⇒9 × 24 = 2(144 - x²)
⇒ 9 × 12 = 144 - x²
⇒ 108 - 144 = - x²
⇒ x² = 36
⇒ x = ±6 , but speed ≠ negative
so, x = 6 km/h

Hence, speed of water current is 6 km/h

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