SOLUTION: each of two brothers can wash a car in 1 hour, however, their sister can was the car in 45 mins. if all three work together, how long will it take to wash the car?

Question 908158: each of two brothers can wash a car in 1 hour, however, their sister can was the car in 45 mins. if all three work together, how long will it take to wash the car?
Answer by richwmiller(17219) (Show Source): You can put this solution on YOUR website!
a=1 b=1 c=0.75
1/a+1/b+1/c=1/x
1/1+1/1+1/0.75=1/x
0.75/0.75+0.75/0.75+1.0/0.75=1/x
2.5/0.75=1/x
x=0.75/2.5
x=.3 hours working together
.3 hours is 3/10*60=18 minutes
check
1/a+1/b+1/c=1/x
1/1+1/1+1/0.75=1/0.3
0.75/0.75+0.75/0.75+1.0/0.75=1/0.3
2.5/0.75=1/0.3
0.75/2.5=0.3
0.3=0.3
ok
18/60+18/60+18/45=1
54/180+54/180 +72/180=1
180/180=1

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