Question

A motorboat goes downstream and covers a distance in 4 hours while it covers the same distance upstream in 5 hours if the speed of the stream is 3 kilometre per hour find the speed of the motor boat in still water​

Answer 1

Answer:

let the speed of boat in still water be xkm/hr and and speed of stream be ykm/hr

let the speed in downstream be(x+y)km/hr

and in upstream be (x-y)km/hr

time=distance/speed

t1=3/x+y

4x+4y=3........(1)

t2=3/x-y

5x-5y=3...........(2)

multiplying eq.(1)by 5,we get

20x+20y=15........(3)

multiplying eq.(2)by 4,we get

20x-20y=15..........(4)

adding eq.3 and 4,we get

20x=30

x=1.5

putting the value of x in eq.3

20*1.5+20y=15

30+20y=15

y=0.75