Question 249668
If Sally can paint a house in a 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 together?
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Use product/sum
= 4*6/(4+6) = 24/10
= 2.4 hours.
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The long way:
S does 1/4 of the house per hour.
J does 1/6 per hour.
Together, they do 1/4 + 1/6 per hour = 5/12
5/12 house per hour --> 12/5 hours per house
= 2.4 hours.