SOLUTION: Hi, could you tell me how to set up a problem like "You can wash one window in 15 minutes and your sister can wash one window in 20 minutes. How many minutes will it take to wash 1

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Question 657668: Hi, could you tell me how to set up a problem like "You can wash one window in 15 minutes and your sister can wash one window in 20 minutes. How many minutes will it take to wash 12 windows if you work together?"
All I need to know is how to set it up.
Thanks!
Found 3 solutions by solver91311, Edwin McCravy, ankor@dixie-net.com:
Answer by solver91311(24713) About Me  (Show Source):
You can put this solution on YOUR website!


If you can do one whole job in time periods, you can do th of the job in one time period.

So, specifically for your problem, you can do th of a window in one minute, and sister can do th of a window in one minute. Working together you can do of a window in one minute.

A little algebra music:

ths

of a window in one minute, so the two of you working together can do one window in or a little more than 8 and a half minutes.

Multiply by 12 to get your time to do all 12 windows.

John

My calculator said it, I believe it, that settles it
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Answer by Edwin McCravy(20060) About Me  (Show Source):
You can put this solution on YOUR website!
You might like this way better:
-----------------------------------------------------------
Your rate is 1 window per 15 minutes, or %281_window%29%2F%2815_minutes%29

Her rate is 1 window per 20 minutes, or %281_window%29%2F%2820_minutes%29

Your and her combined rate is 12 windows per x minutes, or 12_windows%2F%28x_minutes%29

    The equation comes from

             your rate + her rate = your combined rate

                          1%2F15 + 1%2F20 = 12%2Fx
Multiply thru by LCD = 60x

                          4x + 3x = 720
                               7x = 720
                                x = 102 6/7 minutes or about 
1 hour 43 minutes.      

Edwin

Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
You can wash one window in 15 minutes and your sister can wash one window in 20 minutes.
How many minutes will it take to wash 12 windows if you work together?"
:
Let t = time required for both of you to wash 12 windows
:
t%2F15 + t%2F20 = 12
multiply by 60 to get rid of the denominators, results:
4t + 3t = 60(12)
7t = 720
t = 720/7
t ~ 103 minutes, or 1 hr 43 min