SOLUTION: Jerry and Sam are laying a hardwood floor. Working alone, Jerry can do the job in 20 hours. If the two of them work together, they can complete the job in 12 hours. How long would

Algebra ->  Rate-of-work-word-problems -> SOLUTION: Jerry and Sam are laying a hardwood floor. Working alone, Jerry can do the job in 20 hours. If the two of them work together, they can complete the job in 12 hours. How long would      Log On


   

Question 737174: Jerry and Sam are laying a hardwood floor. Working alone, Jerry can do the job in 20 hours. If the two of them work together, they can complete the job in 12 hours. How long would it take Sam to lay the floor working alone?
I need help which math formula to use and how to perform steps for that formula.

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
The key is to know that you add their rates of
working to get their rate of working together
Let +t+ = Sam's time in hrs to do the job working alone
Jerry's rate: ( 1 job ) / ( 20 hrs )
Sam"s rate: ( 1 job ) / ( t hrs )
rate working together: ( 1 job ) / ( 1 hrs )
----------------------
+1%2F20+%2B+1%2Ft+=+1%2F12+
Multiply both sides by +12%2A20%2At+
+12t+%2B+12%2A20+=+20t+
+8t+=+240+
+t+=+30+
Sam would take 30 hrs to do the job working alone
check:
+1%2F20+%2B+1%2Ft+=+1%2F12+
+1%2F20+%2B+1%2F30+=+1%2F12+
+3%2F60+%2B+2%2F60+=+5%2F60+
+5%2F60+=+5%2F60+
OK