Question

A boat having speed of 12km per hour in still water takes 2hours more to go 32km upstream than to return downstream to the same spot what is the speed of stream ​

Answer 1

let speed of stream =x

speed of motorboat = 12 km/h

distance= 32km

time taken by motorboat to go downstream= 32/(x+ 12) h

time taken to go upstream = 32/(12-x)

32/(x+12) + 2 = 32/(12- x)

=32/(12- x) - 32/(x+12) = 2

=32(x+12) - 32(12-x) = 2(12-x)(x+12)

=32x + 32*12- 32*12+ 32x = 288 - 2x2

=64x= 288 - 2x2

=32x= 144-x2

= x2 +32x - 144=0

=x2 - 36x + 4x - 144= 0

= (x + 4) • (x - 36)=0

= x -36= 0 or x+4=0

= x=36km/h as x cant be -4 which is negative

so speed of stream is 36km/h