Elf toy problem: how long when working together?

[silverbleach]

Problem:Alyssa and Zachary are two of Santa's elves. Alyssa can make a toy in twelve hours, and Zachary can make the same toy in seven hours. How long would it take Alyssa and Zachary if they were to make the toy together?

Any one know the process in figuring this out? Or the answer? Or better yet the process and answer?

 

[stapel]

You could use the standard process, probably displayed in your textbook and/or in your classnote, of converting the times to rates.

If the one takes twelve hours to complete the job, how much does she do in one hour? How much does the other do in an hour. How much then can they do together in one hour (pretending this were something they could "combine" on, which it isn't)?

If they can do that much in one hour, how many hours do they need to finish the job?

If you get stuck, or if your class is using a different method, please reply showing your work. Thank you.

Eliz.