SOLUTION: George needs 30 minutes to clean 120 plates. Christian needs 20 minutes to clean 120 plates. How much time will they need to clean the plates if they work together?

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Question 1089728: George needs 30 minutes to clean 120 plates. Christian needs 20 minutes to clean 120 plates. How much time will they need to clean the plates if they work together?
Answer by ikleyn(52781) About Me  (Show Source):
You can put this solution on YOUR website!
.
This problem is for easy MENTAL solution. 

    George cleans 120%2F30 = 4 plates each minute.

    Christian cleans 120%2F20 = 6 plates each minute.

    Working together, they clean 4 + 6 = 10  plates each minute.


    Hence, it will take 12 = 120%2F10 minutes for them to complete the job working together.

Solved.

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It is joint-work problem.

There is a wide variety of solved joint-work problems with detailed explanations in this site.  See the lessons
    - Using Fractions to solve word problems on joint work
    - Solving more complicated word problems on joint work
    - Selected joint-work word problems from the archive


Read them and get be trained in solving joint-work problems.

Also,  you have this free of charge online textbook in ALGEBRA-I in this site
    - ALGEBRA-I - YOUR ONLINE TEXTBOOK.

The referred lessons are the part of this textbook under the topic
"Rate of work and joint work problems"  of the section  "Word problems".