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

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Question 352577: Each of two brothers can wash a car in 1 hour; however their sister can wash the car in 45 minutes.If all three work together, how long will it take to wash the car?
Found 2 solutions by nerdybill, stanbon:
Answer by nerdybill(7384) (Show Source):
You can put this solution on YOUR website!
Each of two brothers can wash a car in 1 hour; however their sister can wash the car in 45 minutes.If all three work together, how long will it take to wash the car?
.
Rate of each brother: 1 car per 1 hour = 1/1
Rate of sister: 1 car per 45 min = 1 car per .75 hour = 1/.75
.
Let x = time (hours) for all three working together
then
x(1/1 + 1/1 + 1/.75) = 1
x(1 + 1 + 1/.75) = 1
multiplying both sides by .75:
x(.75 + .75 + 1) = .75
x(2.5) = .75
x = .75/2.5
x = .3 hour
or
x = 18 minutes

Answer by stanbon(75887) (Show Source):
You can put this solution on YOUR website!
Each of two brothers can wash a car in 1 hour; however their sister can wash the car in 45 minutes.
If all three work together, how long will it take to wash the car?
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Equation:
rate + rate + rate = together rate
1 + 1 + (1/(3/4)) = 1/x
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2 (4/3) = 1/x
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10/3 = 1/x
x = 3/10 hr
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(3/10)hr = (3/10)60 min = 18 minutes
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They can do it together in 18 minutes.
Cheers,
Stan H.