Suppose the chocolate-flavored sugar is A, the fruit-flavored sugar is B, and the two milk-flavored sugars are C 1 and C2 respectively;

So, now nicknames come up with two kinds of candy, one of which is known to be milk-flavored, so at least one of these two kinds of candy must be milk-flavored, that is, one or both of them are milk-flavored.

If only one is milky, then if the milky one is C 1, then the other one has two possibilities, A or B;

If the taste of milk is C2, there are only two possibilities, A or B, because there is only one taste of milk.

Another example is obviously C 1 and C2.

That is, when it is known that at least one smells like milk, there are five possibilities: a, C 1.

b，c 1；

One, C2;

C2

C2 c 1

So the probability that both tastes like milk is 1/5.

This problem is a typical conditional probability problem. When you go to college, you will learn the method of conditional probability in probability theory and answer this conditional probability question in a more formulaic way.