Question

Pratik takes 8 hours to travel 36 km downstream and return to the same spot. The speed of boat in still water is 12 km. per hour. Find the speed of water current. Solve the word problem

Answer 1

Hi ,

Speed of a boat in still water = 12 kmph

Let speed of the water current = x kmph

Speed of the boat in down stream = ( 12 + x )kmph

Speed of the boat in upstream = ( 12 - x ) kmph

time taken to travelled in up = d/s

t1 = 36/( 12 - x ) ---( 1 )

time taken to travelled in down = d/s

t2 = 36/( 12 + x )---( 2 )

according to the problem given ,

t1 + t2 = 8 hours

36/( 12 - x ) + 36/( 12 + x ) = 8

9/( 12 - x ) + 9/( 12 + x ) = 2

9[ 12 + x + 12 - x ]= 2( 12 + x )( 12 - x )

9 × 24 = 2 ( 12² - x² )

9 × 12 = 144 - x²

108 = 144 - x²

x² = 144 - 108

x² = 36

x = 6

Therefore ,

speed of water current = x = 6kmph

I hope this helps you.

: )