Question

A man rowing at 5 km/hr in still water take thrice as much time in going 40 km. Up the river as in going 40 km down. Find the ratio at which the river flows.

Answer 1

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.

HOPE IT HELPED U MATE !!!!

Answer 2

Let’s assume x to be the speed of the stream.  So, we know that  Speed of boat in downstream = (5 + x) and,  Speed of boat in upstream = (5 – x)  It is given that,  The distance in one way is 40 km.  And,  Time taken during upstream = 3 × time taken during the downstream  Expressing it by equations, we have  40/ (5 – x) = 3 x 40/ (5 + x) [∵ time = distance/ speed]  By cross multiplication, we get  (5+x) = 3(5-x)  ⇒ 5 + x = 3(5 – x) ⇒ x + 3x = 15 – 5  ⇒ x = 10/4 = 2.5  Therefore, the speed of the stream is 2.5 km/hr.