SSC CGL 2022 PYQ — Question 58

The correct answer is Option 3 i.e. 20/27 m/sec.

Given:

Speed of boat in still water, x = $16 \over 3$ km/hr

Concept Used:

Time = Distance/speed

Downstream speed = speed of boat in still water + speed of stream

Upstream speed = speed of boat in still water - speed of stream

Explanation:

Let the speed of stream be y km/hr and distance travelled be D km.

So, Downstream speed = x + y = $16 \over 3$ + y

And

Upstream speed = x - y = $16 \over 3$ - y

Now, according to the given question, 

${D \over (x - y)} = 3({D \over x + y})$

⇒  $16 \over 3$ + y = 3(  $16 \over 3$ - y)

⇒ $16 \over 3$ + y = 16 - 3y

⇒ 4y = 16 - $16 \over 3$

⇒ 4y = $32 \over 3$

⇒ y = $8 \over 3$

Now,

Speed of stream in m/sec = ${8 \over 3} \times {5 \over 18}$ = $20 \over 27$

Hence,

The speed of the stream is $20 \over 27$ m/sec.