SOLUTION: If A can do a job in 5 hrs. and B can do a job in 8 hrs. Together they can do a job in_ hrs.

Algebra ->  Rate-of-work-word-problems -> SOLUTION: If A can do a job in 5 hrs. and B can do a job in 8 hrs. Together they can do a job in_ hrs.      Log On


   

Question 136426: If A can do a job in 5 hrs. and B can do a job in 8 hrs. Together they can do a job in_ hrs.
Found 2 solutions by ptaylor, jeff@yahoo.com:
Answer by ptaylor(2198) About Me  (Show Source):
You can put this solution on YOUR website!
Let x=amount of time it takes A&B to do the job working together
A works at the rate of 1/5 of the job per hour
B works at the rate of 1/8 of the job per hour
Together A & B works at the rate of 1/5+1/8 (LCM is 40)
=8/40 + 5/40=13/40 of the job per hour, so our equation to solve is:
(13/40)x=1 (1 job, that is) multiply each side by 40
13x=40 divide each side by 13
x=3.0769 hours-----------------------time it takes A&B to do the job working together
Hope this helps---ptaylor

Answer by jeff@yahoo.com(1) About Me  (Show Source):
You can put this solution on YOUR website!
Let 1/x= the time of A and B to complete the job. (hours)
rate of A to do the job alone
A=1/5
rate of B to do the job alone
B= 1/8
1/x = 1/5 + 1/8

1/x = 13/40
13x = 40
x = 40/13
x = 3.0769
therefore A and B can do the job in 3.0769 hours