Question

A boat which sails at 10km/hr in still water starts chasing, from 10km behind, another one which sails at 4km/hr in the upstream direction. After how long will it catch up if the stream is flowing at 2km/hr

Answer 1

10km\hr the boat will float

Answer 2

Answer:

2.5 hours

Step-by-step explanation:

Let the point at which they meet be C and that the distance from where the boat ahead is to C is x.

Given the speed of the stream we can get the speed of the second boat upstream.

We have :

Speed of boat 2 = 10 - 2 = 8 km/h

Speed of boat 1 = 4km/h

Time taken by each to reach C is the same.

Time = Distance / speed

Boat 2 travels (x + 10)km to reach C.

Time = (x + 10)/8

Boat 1 travels x km to reach C :

Time = x/4

Since the time is equal in each case we have :

x/4 = (x + 10)/8

8x = 4(x + 10)

8x = 4x + 40

8x - 4x = 40

4x = 40

x = 10

Time = 10/4 = 2.5 hours

It takes 2.5 hours for the boat to catch up with the first boat.