Question 320236
Sally does 1/4 house per hour.
John paints 1/6 house per hour.
Together, they do 1/4 + 1/6 per hour = 10/24 houses per hour.
Hours per house = 24/10 = 2.4 hours
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If you're pressed for time, as on a test, use the shortcut, product/sum
4*6/(4+6) = 24/10
= 2.4 hours