SSC CGL 2022 PYQ — Question 73

The correct answer is Option 1 i.e. $5{{5} \over 27}km$

Given:

Speed of boat in still water = $21{{3} \over 2}$ km/hr = 22.5 km/hr

Speed of stream = 12.5 km/hr

Time = 40 minutes

Concept Used:

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

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

Disatance = speed ×  time

Explanation:

Let the distance of the place be D km.

Now, according to the given question,

${D \over downstream\ speed} + {D \over upstream\ speed} = {40 \over 60}$

⇒ ${D \over (22.5 + 12.5)} + {D \over (22.5 - 12.5)} = {2 \over 3}$

⇒ ${D \over 35} + {D \over 10} = { 2\over 3}$

⇒ ${9D \over 70} = {2 \over 3}$

⇒ $D = {140 \over 27}$ = $5 \frac{5}{27}$ km.

Hence, the distance is $5 \frac{5}{27}$ km.