Question

A boat which has speed of 5 km/hr in still water crosses a river of width 1 km along the shortest possible path in 15 minutes. The velocity of the river water in km/hr is :
a) 4
b) 3
c) 1
d) 2

Answer 1

Did you solve this?

Answer 2

I tried, but didn't get the equation.

Answer 3

Can u say the equation?

Answer 4

Let me see what diagram you've drawn first.
By the way, if x is the river's speed, the final equation will be:
\[\sqrt{25-x ^{2}}*15/60=1\]

Answer 5

Can I post tomorrow? I have to go now to a hospital.

Answer 6

All right! What happened by the way?

Answer 7

Regular checkup, That's all.

Answer 8

@Mani_Jha < can u explain now?

Answer 9

@Aadarsh, the shortest possible path is that straight line marked 1 km. Now if you attempt to move in this line, the flow of the river will deflect you to a longer path.

You attempt to move through AB, but the river deflects you to the path BC, which is longer.
Now try to think: What path must you take, so that, even after the deflection, you take the shortest path AB?
Understood?