A boat can travel 21 km in 3 hours going upstream . It can travel 55 km in 5 hours going downstream . What is the speed of the stream ?

Given, Distance travelled in upstream = 21km Time taken in upstream = 3hours Let, Speed of the upstream = y kmph ( Speed * Time = Distance) y kmph = 21/3 = 7 kmph Given, Distance travelled in downstream = 55km Time taken in downstream = 5 hours Let, Speed of the downstream = x kmph x kmph = 55/5 = 11 kmph Speed of the stream = 1/2(speed of the downstream - speed of the upstream) = 1/2(x-y) =1/2(11-7) = 2 Speed of the stream = 2 kmph