SOLUTION: If joe can paint a fence in 3hrs. and jack can paint it in 4hrs. How long will it take them to paint it together.

Question 258979: If joe can paint a fence in 3hrs. and jack can paint it in 4hrs. How long will it take them to paint it together.
Found 2 solutions by Greenfinch, drk:
Answer by Greenfinch(383) (Show Source): You can put this solution on YOUR website!
Joe does 1/3 per hour, Jack does 1/4 per hour.
In one hour they can paint 1/3 plus 1/4 = 7/12
So time to paint it all is 12/7 or 1 5/7 hours
Answer by drk(1908) (Show Source): You can put this solution on YOUR website!
This is a working together or job / time problem. We use the following formula
(J1/T1)(x) + (J2/T2)(x) = TJ
where
J1 = person 1's job
T1 = person 1's time
J2 = person 2's job
T2 = person 2's time
x = time together
TJ = total number of jobs
--
From the given information we get

--
step 1 - multiply by 12 to get

step 2 combine like terms to get

step 3 - divide to get

So it will take them together 12/7 hrs or ~ 1.71 hours
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