SOLUTION: Norman can collect all grocery carts in the parking lot in 12 minutes. Charles can collect all carts in 18 minutes. How long will it take to collect all carts if Norman and Charl

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Question 308102: Norman can collect all grocery carts in the parking lot in 12 minutes. Charles can collect all carts in 18 minutes. How long will it take to collect all carts if Norman and Charles work together?
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
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Norman can collect all grocery carts in the parking lot in 12 minutes.
Charles can collect all carts in 18 minutes.
How long will it take to collect all carts if Norman and Charles work together?
:
Let t = time required when working together (in min)
:
Let the completed job = 1
:
Each will do a fraction of the job, the two fractions add up to 1
:
t%2F12 + t%2F18 = 1
Multiply by 36 to clear the denominators, results:
3t + 2t = 36
5t = 36
t = 36%2F5
t = 7.2 minutes