SOLUTION: Sarah can paint a fence in 4 hours . her father can paint it in 2 hours . if they work together , how long will it take them ?

Question 654355: Sarah can paint a fence in 4 hours . her father can paint it in 2 hours . if they work together , how long will it take them ?
Answer by schmidtmomto6(24) (Show Source): You can put this solution on YOUR website!
Sarah can paint a fence in 4 hours . her father can paint a fence in 2 hours. If they both painted fences for 4 hours, they would be able to paint 3 fences (her 1 fence plus his 2 fences) So, together, their rate is 3 fences per 4 hours. But, we just want to know how long it takes them to paint 1 fence. So, divide both the numerator of our rate and the denominator of our rate by 3. This will leave us with 1 fence per 4/3 hour (or 4/3 of 60 minutes). The answer, then, is 80 minutes.
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