SOLUTION: It takes Doug 3 days to reroof a house. If Doug's son helps him, the job can be completed in 2 days. How long would it take Doug's son, working alone, to do the job?

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Question 1173832: It takes Doug 3 days to reroof a house. If Doug's son helps him, the job can be completed in 2 days. How long would it take Doug's son, working alone, to do the job?
Found 2 solutions by josgarithmetic, greenestamps:
Answer by josgarithmetic(39616) About Me  (Show Source):
You can put this solution on YOUR website!
Doug, 1%2F3
Son, 1%2Fn
Doug+Son, 1%2F2

1%2F3%2B1%2Fn=1%2F2
-
1%2F2-1%2F3=1%2Fn
3%2F6-2%2F6=1%2Fn
1%2F6=1%2Fn
highlight%28n=6%29

Answer by greenestamps(13198) About Me  (Show Source):
You can put this solution on YOUR website!


The other tutor showed a typical algebraic solution, using the fraction of the job that each worker completes in a day.

Here is a quick informal solution, if formal algebra is not required.

Doug can do the job alone in 3 days, so when he and his son complete the job together in 2 days, Doug does 2/3 of the job.
That means his son does 1/3 of the job in those 2 days.
And that means his son would take 2*3=6 days to do the job alone.