SOLUTION: It takes one man 10 hours to do a certain job. After he has worked for 4 hours, another man is sent to help him. The two men complete the job in 4 hours. How long would it take

Algebra ->  Rate-of-work-word-problems -> SOLUTION: It takes one man 10 hours to do a certain job. After he has worked for 4 hours, another man is sent to help him. The two men complete the job in 4 hours. How long would it take       Log On


   

Question 746589: It takes one man 10 hours to do a certain job. After he has worked for 4 hours, another man is sent to help him. The two men complete the job in 4 hours. How long would it take the second man to do the entire job alone?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Add their rates of working to get their
rate working together
1st man's rate: ( 1 job ) / ( 10 hrs )
Both men working together: ( 1 job ) / ( 4 hrs )
------------
Let +t+ = the time in hours for the 2nd
man to do the job alone
------------
+1%2F10+%2B+1%2Ft+=+1%2F4+
Multiply both sides by +20t+
+2t+%2B+20+=+5t+
+3t+=+20+
+t+=+6.667+ hrs
+.667%2A60+=+40+ min
It takes the 2nd man 6 hrs and 40 min to do the job alone