Question

A boat can go 72 km upstream in 4hours and downstream in 3 hours. Find the speed of:

1. Boat still in water

2. Stream

Answer 1

Let the speed of boat in still water = x km/hr

Speed of stream = y km/hr

While going upstream, speed of boat = (x-y)km/hr

While going downstream, speed of boat = (x+y)km/hr

Now according to question,

We know , speed =

We get, x-y =

x-y = 18 …………….(1)

also, x+y =

x+y = 24 …………….(2)

adding eqn 1 and 2

we get,

2x = 24+18

2x = 42

x = 21

put the value of x in eqn (1)

we get, 21-y = 18

-y = 18-21

-y = -3

Y= 3

Hence, the speed of boat in still water is 21km/hr

Speed of stream = 3km/hr