if sally can paint a house in 4 hours, and john can paint the same house in 6 hours, how long will it take for both oh them to paint the house together?

Sally can paint the house in 4 hours
The rate at which he can paint the house is 1/4 per hour
John can paint the house in 5 hours
The rate is 1/5 hours
Together the rate is 1/4+1/5=9/20
So they can paint the house in 1/(9/20)=20/9 hours =2.22 hours

Together = x

1/x = 1/4 + 1/6
1/x = 3/12 + 2/12
1/x = 5/12
5x = 12
x = 12/5 hrs

-->
2 2/5 hrs
2/5 hrs
= 2/5x 60
= 24 min.

2 hours 24 minutes.