Question 1143029
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There are many different ways to look at problems like this.  Here are a couple of ways that work for me.  Possibly you will get responses from other tutors showing other methods; you might like one of them better....<br>
(1) The 3 cats together catch 3 mice in 3 minutes, so their rate of catching mice is 1 per minute.  So the same 3 cats will catch 99 mice in 99 minutes.<br>
(2) Changing the number of mice from 3 to 99 multiplies the required number of cats by 99/3 = 33.  Then changing the number of minutes from 3 to 99 DIVIDES the required number of cats by 99/3 = 33.  So you end up requiring the same number of cats.