Thread: Why is this the answer???

I can't for the life of me figure out why 2 2/5 is the answer to the following question. If anyone can explain this to me then I would appreciate it.

Question:

John can paint a fence by himself in 6 hours and Jenny can paint the fence in 4 hours. How long will it take them to paint the fence if they work together?

The answer is 2 2/5.

Originally Posted by Runfast1

Question:
John can paint a fence by himself in 6 hours and Jenny can paint the fence in 4 hours. How long will it take them to paint the fence if they work together? The answer is 2 2/5.

So in one hour they can do of the fence.
THUS??

In 1 hour John alone can paint 1/6 of the fence and Jenny can paint 1/4 of the fence. So together in 1 hour they can paint 1/6+1/4 of fence. That is 5/12 of fence. So 1/12 of fence in 1/5 hour and whole fence (12/12) in 12/5 hours.

Thank you so much for the very quick help!