Question

40. A boat requires 6 hours to travel 36 km down stream and 24 km up
stream. The same boat needs 9 hours to travel 40 km up stream and 48
km down stream. Find the speed of the boat in still water and the
speed of the stream.​

Answer 1

Answer:

let the speed of the stream be 'X'

and speed of the boat 'Y'

=36/x+y +24/x-y = 6

=48/x+y + 40/x-y = 9

let 1/x+y=m and 1/x-y=n

=36m+24n=6

=48m+40n=9

=m=6-24n/36 = 1-4n/6

=48(1-4n/6) + 40n = 9

=8-32n + 40n = 9

=8n=1n

=n=1/8

=m=1-4(1/8)/6

=m=1/12

=x-y=8

=x=10

=x+y=12

=y=2

speed of stream = 10km/hr

speed of the boat = 2km/hr