Question

A boat moves at a rate of 13 mph in still water. If the rivers current flows at a rate of 4 mph, how long does it take the boat to travel 20 miles upstream?

It takes ___ hours.

Answer 1

20/9 hours

Explanation:

Note: I'm assuming 'upstream' means against the current.

If the boat flows against the current, it's speed is 13 - 4 = 9 mph.

`(20m)/(9mph) =(20)/(9) hours`

That means our answer is 20/9 hours.

If it is travelling with the current, its speed is 13 + 4 = 17 mph.

Therefore, 20/17 would be our answer if that were the case

Answer 2

• 2 2/9 hours

Explanation:

Speed upstream is reduced:

• 13 - 4 = 9 mph

Time to travel 20 miles:

• 20/9 = 2 2/9 hours