SOLUTION: Kobe completed a certain job in 20 hrs. Together, Kobe and Justin completed the same job in 12 hrs. How long would it take Justin to complete by himself?

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Question 128773: Kobe completed a certain job in 20 hrs. Together, Kobe and Justin completed the same job in 12 hrs. How long would it take Justin to complete by himself?

Answer by checkley71(8403) About Me  (Show Source):
You can put this solution on YOUR website!
20X/(20+X)=12 CROSS MULTIPLY
20X=12(20+X)
20X=240+12X
20X-12X=240
8X=240
X=240/8
X=30 HRS FOR JUSTIN WORKING ALONE TO COMPLETE THE JOB.
PROOF:
20*30/(20+30)=12
600/50=12
12=12