Question

The speed of a stream is 4 mph. A boat travels 6 miles upstream in the same time it takes to travel 14 miles downstream. What is the speed of the boat in still water?

Answer 1

The speed of boat in still water be `10` `mph`.

Explanation:

Let the speed of boat in still water be `x` mph. AS, the speed of stream is `4` mph, upstream speed will be `(x-4)` and downstream speed will be `(x+4)`.

Time taken by boat for travelling `6` miles upstream will be `6/(x-4)` and time taken by boat for travelling `14` miles downstream is `14/(x+4)`.

As the two are equal

`6/(x-4)=14/(x+4)` or `6(x+4)=14(x-4)` or

`6x+24=14x-56`

Hence `14x-6x=24+56=80` or `8x=80`.

Hence `x=10`.