The time taken by a man to travel 36 miles downstream is 90 min less than to go the same distance upstream . The speed of the man in still water is 10 mph. Find the speed of the stream?

The time taken by a man to travel 36 miles downstream is 90 min less than to go the same distance upstream . The speed of the man in still water is 10 mph. Find the speed of the stream? Correct Answer 2 mph

Let, the speed of stream = x mph ATQ, 3610 - x - 3610 + x = 9060⇒36(10 + x) - 36(10 - x)(10 - x)(10 + x) = 32⇒360  + 36x  - 360  +  36x102  - x2 = 32⇒72x100 - x2 = 32⇒144x = 300  - 3x2⇒3x2  + 144x  - 300  = 0  ⇒x2  + 50 x  - 2x  - 100 = 0⇒x(x + 50)  - 2(x + 50) = 0⇒(x - 2) (x + 50) = 0 x - 2 = 0 or , x + 50  = 0  ⇒x = 2 ⇒x  = - 50 .'. The speed of the stream  =  2mph