The reason for this is the following：

As we all know, when two coins are thrown at the same time, there can only be two results: one is positive, the other is negative and the other is positive or negative.

So the probability of one positive and one negative is 1/2, and the probability of the same positive or negative is 1/2. The probability is equal, so it is fair.

Because the second situation also includes two situations, both coins are heads, accounting for 1/2 of the second situation, that is, (1/2 *1/2) =1/4 100 times.

So both coins are heads, which is about 100* 1/4=25 (times).