Originally Posted by

**Dittohead not!**
Since all of the answers are whole numbers, it follows that x + y has to be a factor of ten.

And if Y > X, then it follows that Y > 1, both numbers being integers.

That narrows X + Y down to either 5 or 10.

If x + y = 5, and if x = 1, then the first expression is 1/5 of 10 = 2.

Then the second expression is 4/5 of 20 = 16.

Therefore, the result could be 18, D.

Now, here's another puzzle, one that is more closely related to the conversation about percentages and probabilities:

One population of rats has 50,000 females. 1/10 of the females eat their young.

(Yes, rats really do this at times, but this is about math, not biology.)

The other population has half a million females. 10% of the females eat their young.

So, in population A, 1/10 of 50,000, or 5,000 litters are eaten by their mothers.

In population B, 10% of half a million, or 50,000 litters are eaten by their mothers.

So, a given baby rat is:

A. More likely to be eaten if born into population A.

B. More likely to be eaten if born into population B.

C. Equally likely to be eaten regardless of which population births it.