SOLUTION: A worker can build a fence in 16 hours. With the help of an assistant, the fence can be built in 9 hours. How long should it take the assistant, working alone, to build the fence?

Algebra ->  Algebra  -> Expressions-with-variables -> SOLUTION: A worker can build a fence in 16 hours. With the help of an assistant, the fence can be built in 9 hours. How long should it take the assistant, working alone, to build the fence?      Log On

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Question 129954: A worker can build a fence in 16 hours. With the help of an assistant, the fence can be built in 9 hours. How long should it take the assistant, working alone, to build the fence?
Answer by josmiceli(6793) About Me  (Show Source):
You can put this solution on YOUR website!
Let a = assistant's time to build fence
In words:
(1 fence)/(worker's time) + (1 fence)/ (assitant's time) =
(1 fence) / (time for both working together)
1%2F16+%2B+1%2Fa+=+1%2F9
multiply both sides by 9%2A16%2Aa
9a+%2B+9%2A16+=+16a
9a+%2B+144+=+16a
7a+=+144
a+=+20.57
It takes the assistant 20 hrs and 34 minutes approximately