|
Question 374925: It takes John 20 hours to paint a building. It takes Sam 15 hours to paint the same building. How long will it take for them to paint the building if they work together, with Sam starting one hour later than John?
Found 2 solutions by solver91311, edjones:
Answer by solver91311(24713)   (Show Source):
You can put this solution on YOUR website!
If A can do a job in x time periods, then A can do  of the job in 1 time period. Likewise, if B can do the same job in y time periods, then B can do  of the job in 1 time period.
So, working together, they can do
of the job in 1 time period.
Therefore, they can do the whole job in:
time periods.
However, since John has been working for an hour before Sam starts to help him, John has completed  of the job already. That means that there are  of the job remaining when Sam starts. If it takes Sam 15 hours to do the entire job by himself, then it would take him  hours to do the remaining part of the job by himself. And quite obviously it would take John 19 hours to finish by himself.
So just do the process outlined using  hours and  hours as the times for the whole job. And don't forget to add back the hour that John has already been working.
John
My calculator said it, I believe it, that settles it
Answer by edjones(8007)  (Show Source):
You can put this solution on YOUR website! John does 1/20 of the job in the 1st hr.
x/20 + x/15 = 19/20 John has already done 1/20 of the job.
3x+4x=57 Multiply each side by 60.
7x=57
x=57/7 hrs together after John worked alone for one hr.
.
Ed
|
|
|
| |
