question: There were 50 cats on a rock. Four boats came and carried away 5 cats each, and later, 3/5 of the remaining cats ran after a mouse they'd seen. How many cats were left on the rock?
answer: When four boats carried away 5 cats each, the total number of cats that left the rock is 4*5 = <<4*5=20>>20 cats.
  The number of cats remaining on the rock became 50-20 = <<50-20=30>>30.
  Later 3/5 of the remaining cats left the rock and ran after a mouse, a total of 3/5*30 = <<3/5*30=18>>18 cats.
  The number of cats that remained on the rock is 30-18 = <<30-18=12>>12 cats
  #### 12