SOLUTION: A crew working on a section of road can finish it in 20 hours. Another crew can finish it in 12 hours. How long will it take them both together? I am 56 years old and working on ge

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Question 868397: A crew working on a section of road can finish it in 20 hours. Another crew can finish it in 12 hours. How long will it take them both together? I am 56 years old and working on getting my high school diploma i could really use some help please. Thank You
Answer by josgarithmetic(39620) About Me  (Show Source):
You can put this solution on YOUR website!
A uniform rates job or task completion problem. The basic numerical idea is R%2AT=J and the variables mean Rate, Time, Job.
The units for each variable as dimensions are:
R, jobs per time
T, time
J, number of jobs or amount of a job

A_crew works at the rate of 1%2F20 jobs per hour.
Another_crew works at the rate of 1%2F12 jobs per hour.

The question you want to answer is, "How long will it take them both together?"
The sum of the crews rates is the rate for both crews working together on the same job. This means, you can form this equation:
Let R = combined rate of both crews while they work together on the same job.
highlight%28highlight%281%2F20%2B1%2F12=R%29%29.
Just compute R.

Be sure to understand that the unit of R in that equation will be JOBS per HOUR, or "A SECTION OF ROAD per HOUR". If you want how much time for this one section of road, then you will want the reciprocal of R.