SOLUTION: Printing Press A starts working on a job at 8:00 am. Working alone, press A would take 24 hours to do the job. At 9:30 am, press B also begins to run the same job as A. Press B is

Algebra ->  Rate-of-work-word-problems -> SOLUTION: Printing Press A starts working on a job at 8:00 am. Working alone, press A would take 24 hours to do the job. At 9:30 am, press B also begins to run the same job as A. Press B is       Log On


   



Question 621276: Printing Press A starts working on a job at 8:00 am. Working alone, press A would take 24 hours to do the job. At 9:30 am, press B also begins to run the same job as A. Press B is twice as fast as press A. What time will the job be completed?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
How much of the job did press A get done in 1.5 hrs
from 8 AM to 9:30 AM?
A's rate is ( 1 job ) / ( 24 hrs )
In 1.5 hrs:
+%281%2F24%29%2A1.5+=+.0625+ job/hr
Now both A and B work on job
There is +1+-+.0625+=+.9375+
of the job left to do.
B's rate is ( 1 job ) / ( 12 hrs )
+1%2F24+%2B+1%2F12++=+.9375+%2F+t+
Multiply both sides by +24t+
+t+%2B+2t+=+22.5+
+3t+=+22.5+
+t+=+7.5+
In 7.5 hrs after B starts, the job is done
9:30 + 7.5 = 5 PM job is done
check answer:
+1%2F24+%2B+1%2F12++=+.9375+%2F+t+
+1%2F24+%2B+1%2F12++=+.9375+%2F+7.5+
+1%2F24+%2B+2%2F24+=+.125+
+1%2F8+=+.125+
+.125+=+.125+
OK