Gena's crocodile, the old woman Shopoklyak and the Cheburashka decided to prepare the platform on which they will build the house for friends, Gena working as one the Cheburashka in 20 hours, and Shopoklyak in 15 hours can perform work in 12 hours. For what is the time they will perform this work in common?

1 - all platform 1/12+1/20+1/15=5/60+3/60+4/60=12/60=1/5 a part of the platform all together in 1 hour 1:1/5=5 (h) will prepare Answer: they will perform this work in common in 5 hours
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