Question: I'm completely lost with this math problem: 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?
Can you give me a hand?
Answer: 
When four boats carried away 5 cats each, the total number of cats that left the rock is 4*5 = 20 cats.
The number of cats remaining on the rock became 50-20 = 30.
Later 3/5 of the remaining cats left the rock and ran after a mouse, a total of 3/5*30 = 18 cats.
The number of cats that remained on the rock is 30-18 = 12 cats