sally can paint a house in 4 hours -
john can paint the same house in 6 hourse -
together -
sally can paint a house in 4 hours and john can paint the same house in 6 hourse how long does it take for them to paint the same house together. I know the answer in 2 hours and 24 mins. and I know that we use D=RT but I can not get 2 hours and 24 mins from it. Please help. thank you.
4 hours = 4* 60 = 240 minutes
6 hours = 6*60 = 360 minutes
1/240 + 1/360 = 1/t
(multiply both side by t): t/240 + t/360 = 1
(get common denominator): 3t/720 + 2t/720 = 1
5t/720 = 1
(multiply both sides by 720) 5t = 720
(divide both sides by 5) t = 720/5
t = 144 minutes
(convert to hours):
t = 144/60 = 2 hours + (144 – 120 minutes) = 2 hours 24 minutes