SOLUTION: Problem: a person can wash their car in 30 minutes. A friend can do it in 20 minutes. How long will it take them if they work together. I really have a tough time with wo

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Question 56227: Problem:
a person can wash their car in 30 minutes. A friend can do it in 20 minutes. How long will it take them if they work together.
I really have a tough time with word problems. thank you!
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
a person can wash their car in 30 minutes. A friend can do it in 20 minutes. How long will it take them if they work together.
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You have to understand the difference between time and rate.
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Amount of time for 1st person = 30 min./job ; rate = (1/30) job/min
That means every minute the person does 1/30th of the job.
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Amount of time for the friend= 20 min/job ; rate = (1/20)job/min.
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Amount of time to do job together = x min/job ; rate =(1/x) job/min
EQUATION:
rate of 1st + rate of friend = rate together
1/30 + 1/20 = 1/x
Multiply thru by 60x to get:
2x + 3x =60
5x=60
x=12 minutes (this is the time they will take working together)
Cheers,
Stan H.