SOLUTION: Each of two brothers can wash a car in 1hr; however, their sister can wash the car in 45 min. If all three work together, how long will it take to wash the car?

Question 908155: Each of two brothers can wash a car in 1hr; however, their sister can wash the car in 45 min. 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/.75=1/x
0.75/.75+.75/.75+1/.75=1/x
2.5/0.75=1/x
0.75/2.5=x
0.3 hours working together
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

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