Question

A man can row 8 km/hr in still
water. If the speed of the current
is 2 km/hr and it takes 4 hours to
a man to row a place and come
back, then how far is the place?
10:06 AM​

Answer 1

Answer :

=> 15 km

Explanation :

⇒ A man can row 8 km/hr in still  water,

   i.e., speed of boat = 8 km/hr

⇒ The speed of the current  is 2 km/hr

   i.e., speed of water = 2 km/hr

⇒ it takes 4 hours to  a man to row a place and come  back

   i.e., total time (upstream and downstream) = 2 hours

Let distance be "x" km

UPSTREAM :

 speed of boat = 8 - 2 = 6 km/hr

 time taken to travel upstream = distance/speed

                                                   = x/6

DOWNSTREAM :

 speed of boat = 8 + 2 = 10 km/hr

 time taken to travel downstream = distance/speed

                                                        =  x/10

total time = 4 hours

$\frac{x}{6} +\frac{x}{10} =4 \\\\ \frac{10x+6x}{60} =4 \\\\ \frac{16x}{60} =4 \\\\ 16x=4 \times 60 \\\\ 16x=240 \\\\ x=240/16 \\\\ x=60/4 \\\\ x=15 km$

=> distance = 15 km