Question

A motorboat in still water travels at a speed of 36kmph. It goes 56 km upstream in 1 hour 45 minutes. The time taken by it to cover the same distance downstream will be
A. 2 hours 45 minutes
B. 3 hours
C. 1 hour 24 minutes
D. 2 hours 21 minutes​

Answer 1

Answer:

C.time=1 hr 24 minute

Step-by-step explanation:

let  speed of stream=x

Then speed of boat in upstream=36-x

time=distance/speed

1 hr 45 min =56/(36-x)

1.75=56/(36-x)

1.75(36-x)=56

1.75*36-1.75x=56

1.75x=63-56=7

so speed of stream=7/1.75= 4 kmph

thus speed of boat in downstream

=36+4=40 kmph

time =d/v

=56/40

=7/5

=1.4 hrs

=1 hr +0.4*60

time=1 hr 24 minute