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Fred and John want to paint Fred's motorboat.  Fred can do it in 3 hours, and John can do it in 6 hours.  How long will it take them working together?

 May 10, 2020
 #1
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1/3  +  1/6 =1/J

J = 2 hours working together.

 May 10, 2020
 #2
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Understand that there is one job. 

 

 

Fred works at a rate of   1  job                   2  job 

                                      ———   call this   ———   to enable you to add it to John's rate

                                        3  hr                    6  hr 

 

 

John works at a rate of   1  job 

                                      ——— 

                                        6  hr 

 

 

Add them together and you get   3  job                  1 job 

                                                   ———  which is   ———    together they do the job in 2 hours   

                                                     6 hr                     2 hr 

 

 

This kind of problem was so hard for me when I was in school.  It took me forever to grasp how to do it. 

.

 May 10, 2020

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