Question

40.) A motorboat travels 10 km downstream in 50 minutes and returns in 1 hour. What is the speed of the motorboat in still water?

(A) 8 km/h (B) 10 km/h (C) 11 km/h (D) 12 km/h​

Answer 1

Given, speed of boat = 10 km/h

Let speed of flow of river = x km/h

Upstream speed of boat = (10 - x) km/h

and downstream speed of boat

According to question,

= (10 + x) km/h

9110−x+9110+x=209110−x+9110+x=20

91(10+x+10−x)(10−x)(10+x)=2091(10+x+10−x)(10−x)(10+x)=20

91(20)100−x2=x2−991(20)100−x2=x2−9

x = 3