SOLUTION: Ingrid can rake our lawn in 90 min ad I can do it in 60 min. If she rakes for 15 min before I join her, how long will it take us to finish? PLEASE HELP!!! The answer is 30 min, but

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Question 125307This question is from textbook algebra: structure and method: book1
: Ingrid can rake our lawn in 90 min ad I can do it in 60 min. If she rakes for 15 min before I join her, how long will it take us to finish? PLEASE HELP!!! The answer is 30 min, but I don't know how to get there. HELP IS MUCH APPRICIATED!!!!!!!!! This question is from textbook algebra: structure and method: book1

Answer by ankor@dixie-net.com(22740) (Show Source):
You can put this solution on YOUR website!
Ingrid can rake our lawn in 90 min and I can do it in 60 min. If she rakes for 15 min before I join her, how long will it take us to finish?
:
Let x = time (in min) for you to finish the job
:
Let the completed job = 1
:
+ + = 1
:
Multiply equation by 180 to get rid of the denominators:
180* + 180* + 180* = 180(1)
Cancel the denominators and you have:
:
2(15) + 2x + 3x = 180
:
30 + 2x + 3x = 180
:
2x + 3x = 180 - 30
:
5x = 150
x =
x = 30 min