SSC CGL 2023 PYQ — Question 58

The correct answer is option 3 i.e. 8 km/h.

Let the upstream speed of the boat be U km/h and downstream speed be D km/h.

According to the given question,

${20 \over U} + {44 \over D}$ = 8    ....(i)

And ${15 \over U} + {22 \over D}$ = 5    ....(ii)

Multiplying equation (ii) by 2 and subtracting equation (i) from equation (ii),

${30 \over U} + {44 \over D}$ = 10

${20 \over U} + {44 \over D}$ = 8

⇒ $10 \over U$ = 2

⇒ U = 5 km/h

Using this value in equation (i),

⇒ ${20 \over 5} + {44 \over D}$ = 8

⇒ D = 11 km/h

So, the speed of boat in still water = ${U + D} \over 2$

⇒ ${5 + 11} \over 2$ = 8 km/h

Hence the speed of boat in still water is 8 km/h.