A person, rowing at the rate of 5 km/hr in still water, takes thrice as much time in going 40 km upstream as in going downstream. Find the speed of the stream.

Pls tell how to solve this

Let the speed of the stream be xkm/hr

Given that speed of the boat is 5km/hr

Therefore, speed of the boat in downstream= (5+x)km/hr

Speed of the boat in upstream= (5-x) km/hr

A/q

Time taken by boat in going 40km upstream is thrice the time taken by the  boat in the downstream   

 Thus,

          40/(5-x)= 3{40/(5+x)}

          40/(5-x)= 120/(5+x)

          200+40x= 600-120x

          120x+40x= 600-200

         160x = 400

          Therefore, x= 2.5km/hr

Hence, speed of the stream is 2.5km/hr.