SOLUTION: I'm in freshman honors algebra at my high school, and I was wondering if you could provide an eqaution to solve and explain it. The question is: A man can do a piece of work in 9 h

Algebra ->  Rate-of-work-word-problems -> SOLUTION: I'm in freshman honors algebra at my high school, and I was wondering if you could provide an eqaution to solve and explain it. The question is: A man can do a piece of work in 9 h      Log On


   

Question 395590: I'm in freshman honors algebra at my high school, and I was wondering if you could provide an eqaution to solve and explain it. The question is: A man can do a piece of work in 9 hours. After he worked 3 hours alone, he was joined by his son, and they finished the job in 4.5 hours. How many hours would it take to do the job alone?
Answer by robertb(5830) About Me  (Show Source):
You can put this solution on YOUR website!
Let s = # of hours it takes the son to do the work alone.
Then 3%2F9++%2B+4.5%281%2F9++%2B+1%2Fs%29+=+1
<==> 7.5%2F9+%2B+4.5%2Fs+=+1
<==> 4.5%2Fs+=+1.5%2F9 ==> s = 27, after cross multiplication.