Question

a Boat can go 24 km downstream and 12 km upstream in a total of 4 hours if speed of boat in still water is 9km/hr Find speed of stream?

Answer 1

let the speed of water stream is x.
then according to question
24/9+x+12/9-x=4

216-24x+108+12x/81-x^2=4
108-12x=324-4x^2
4x^2-12x-216=0
4x^2-36x+24x-216=0
4x(x-9)+24(x-9)=0
x=9 or x=-24.
hence speed of stream will be 9km/hr
because speed can't be in negative