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andreev551 [17]
3 years ago
15

Bob and sarah need to paint a fence. bob can paint the fence in 4 hours and sarah can paint the fence in 2.5 hours. if they work

together, how long will it take them to paint the fence?
Mathematics
1 answer:
zysi [14]3 years ago
7 0
If Bob can paint the fence in 4 hours, then in 1 hour he gets 1/4 of the fence painted.  If Sarah can paint the fence in 2.5 hours, then she gets 2/5 of the fence painted in one hour (1/2.5 = 2/5).  We add those amounts together and set them equal to 1/x, x being the the total time it will take them to paint the whole fence.  1/4 + 2/5 = 1/x.  Find a common denominator first, then add the left side together.  5/20 + 8/20 = 1/x.  13/20 = 1/x.  Cross-multiply to get 13x = 20 and x = 1.54 hours, just a bit over an hour and a half.
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