SSC CGL 2023 PYQ — Question 52

The correct answer is option 2 i.e. $\frac{1}{2}$.

Given that:

The speed of the boat down the stream is 125% of the speedof boat in still water.

Let the speed of the boat in still water and speed of stream be x and y respectively.

According to the question:

Downstream speed = x + y = $125x \over 100$

⇒ x + y = 1.25 x

⇒ 0.25x = y

⇒ x = 4y

If the boat takes 30 minutes to cover 20 km in still water then,

x = $20 \over 30$ × 60 = 40 km/h

So,

y = $40 \over 4$ = 10 km/h

Now,

Upstream speed = x - y = 40 - 10 = 30 km/h

Hence,

Time taken to cover 15 km upstream = $15 \over 30$ = $\frac{1}{2}$ hr