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Hi
three men paint a house in 5 days
 1/5 of the house gets painted each day 
(with each of the three men painting 1/15 of it per day)
How long 'x' will it take 2 men to paint the house?
  x/15 + x/15 = 1
   2x/15 = 1
    2x = 15
     x = 15/2     7 1/2 days