A boat covers 32km upstream and 36 km downstream in 7 hours. Also, it covers 40 km upstream and 48 km downstream in 9 hours. Find the speed of the boat in still water and that of the stream.

Let the speed of the boat in still water and speed of stream be a km/hr & b km/hr respectively.

In case of upstream;

speed = speed of boat – the speed of stream = a – b

In case of downstream;

speed = speed of boat + speed of stream = a + b

As, distance = speed x time,

According to the question,

...... (i)

Also,

Solving (i) x5 – (ii);

a + b = 12 ...... (ii)

Putting this in (i)

⇒ a – b = 8 ...... – (iii)

Adding ((ii)&(iii)

⇒ 2a = 20

⇒ a = 10;

⇒ b = 2

So, speed of boat in still water is 10 km/hr

and speed of stream is 2km/hr