SOLUTION: You must leave for campus in 10 minutes or you will be late for your Algebra test. Unfortunately, you are snowed in. You can shovel the entire driveway in 15 minutes. Your broth

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Question 58652: You must leave for campus in 10 minutes or you will be late for your Algebra test. Unfortunately, you are snowed in. You can shovel the entire driveway in 15 minutes. Your brother can do it in 20 minutes. If you shovel together, how long will it take to clear the driveway?
I keep trying to use the average time but I know it isn't correct.
15+20=35/2=17.5 minutes
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
You must leave for campus in 10 minutes or you will be late for your Algebra test. Unfortunately, you are snowed in. You can shovel the entire driveway in 15 minutes. Your brother can do it in 20 minutes. If you shovel together, how long will it take to clear the driveway?
:
Let t = time (in minutes) required when you work together:
Let the completed job = 1
:
t%2F15 + t%2F20 = 1
:
Clear the denominators, mult eq by 60, resulting in:
4t + 3t = 60
7t = 60
t = 60/7
t = 8.57 minutes, you can just make it.
:
Check:
8.57%2F15 + 8.57%2F20 =
.571 + .4285 = .9995, close enough to 1, don't you think?