Question

It takes Nate four hours to paint a wall, and it takes Jill seven hours to paint the same wall. About how many hours will it will take if Nate and Jill work together to paint the wall?

Answer 1

Rate=1/time
N=1/4 and J= 1/7
TotalN+J= \1/4 + 1/7 = 11/28

Then:
Time = 1/rate = 1/(11/28) = 28/11 hours = 2 6/11 hours= about 2.545 hours. 

Answer 2

2.5 hours if my math is correct!

Hope this helps!!