Bill can finish a job in 3 hours. Minnie can complete the same job in 2 hours. If both of them work together on the same job, how long does it take them to complete the job?

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in an hour, bill can do 1/3 job, Minnie can do 1/2. Both of them can do 1/3+1/2 = 5/6 (in one hour) we can wright a proportion: 5x/6=6/6 30x=36 x=36:30=6/5=1,5 In 1,5 hour they can complete the work together  

dont you add then divide?