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 of them to paint the house?

Question

the answer is 2 hrs and 24 min. How did they come up with that?

Answer 1

In twelve hours, sally can paint 3, and john 2, or five houses together.

combined rate=5houses/12hours

1house=rate*time=5/12 * time
time= 12/5 hrs