SOLUTION: It takes Ralph 12 hours to paint a fence alone. Lisa can do the same job in 16 hours. If Ralph paints alone for 15 minutes before Lisa begins helping, how long must they work toget

Question 907240: It takes Ralph 12 hours to paint a fence alone. Lisa can do the same job in 16 hours. If Ralph paints alone for 15 minutes before Lisa begins helping, how long must they work together to finish painting the fence? Give your answer as a simplified fraction.
Answer by richwmiller(17219) (Show Source): You can put this solution on YOUR website!
c/a+ x/a+x/b=1
(15/60)*1/12+ x/12+x/16=1
0.25*1/12+x/12+x/16=1
x/12+x/16=1-0.25/12
x/12+x/16=0.97916667
x/12+x/16=11.75/12
16x/192+12x/192=188/192
28x/192=188/192
28x=188
x=188/28
x=47/7 this is the simplified fraction

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