Question

2. A boat is moving at the rate of 5km/h in still water, takes thrice as much as time in going 40 km upstream as in going 40 km downstream. Find the speed of the stream.

Answer 1

let the speed in stream=xkm/h
then in upstream it will=(5+x)
in downstream=(5-x) so
distance=40km so,
40/(5-x)=40*3/(5+x) then
200+40x=600-120x
120x+40x=600-200
160x=400
x=400/160
=25 ans

Answer 2

upstream
distance= 40km
speed=3x -5
time = distance/speed
time=40/3x-5

now,downstream
distance=40km
speed=3x-5
time = distance/ speed
time =40/3x+5

40/3x-5=40/3x+5
40(3x-5)=40(3x+5)
120x - 200=120x+200
120x-120x= 200 +200
=400min = 400/60 =