SOLUTION: Jen cleans up the kitchen in 20 minutes, her brother Jen does it in 12 minutes, but Ben, their younger sibling, can mess up the kitchen in ten minutes. How many minutes does it tak

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Question 665546: Jen cleans up the kitchen in 20 minutes, her brother Jen does it in 12 minutes, but Ben, their younger sibling, can mess up the kitchen in ten minutes. How many minutes does it take for the three of them to clean the kitchen?
Answer by bloggauta(8) About Me  (Show Source):
You can put this solution on YOUR website!
(1k/20min)+(1k/12min)+(1k/10min)
= 1/20 + 1/12 + 1/10 = (3+5+6)/60
= 14/60= 7/30 → 7k/30min → 1k/(30/7)min
then the three clean up the kitchen in (30/7)min