Question 1145230
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The easiest path to the answer is logical reasoning.<br>
From the first scenario to the second, the number of rats and the number of minutes are both increased by the same factor (100:3); that means the number of cats required is the same.<br>
ANSWER: 3 cats<br>
(Realistically, however, I think the cats would get rather tired after about 5 or 6 rats....)<br>
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Added later....<br>
You have seen three very different good ways to solve the problem.  When you have more problems like this to solve, try the different methods and find what "works" for you....