Both you and the other user (Xest), confuse joint probabilities for multiple independent events, with probabilities for a single independent event. The probability of a single independent event does not change. This is elementary probability theory.

Perhaps a simple example will help you. Let's say that your wife is pregnant with your first child. The probability to be a boy is 0.5. The child is born and it is really a boy. Congratulations! Now the probability to be a girl is zero! Some years later your wife is pregnant again. What is the probability to have again a boy? Well, it is again 0.5! Some assume that we have to multiply 0.5*0.5=0.25. No, that's wrong! The probability for the first child to be a boy is now 1 (one!) since it is a known fact! The probability for the first child to be a girl is zero. So, even if you want to multiply, you should do 1*0.5=0.5 and you get the same result.

However, this way of thinking is wrong anyway, because it is confusing. We do not have joint probabilities here. There is no way that a previous child can influence the gender of the next child. You should not multiply anything because there is no causal relationship. It does not matter if it is your first, second or tenth child. There is always probability 0.5 for the next child, no matter how many children the woman had before. This is common sense, and it is also formal mathematics.

It is different when you want to compute JOINT probabilities, that is TWO or more events to happen simultaneously. Yes, the probability to have two boys is 0.25. But if you KNOW that one is a boy, then you do not have joint probabilities any more. You just have the probability for one child to be a boy, that's 0.5. If you insist to use joint probabilities, then you have to multiply by one 1*0.5=0.5. It is a completely different question to ask "what is the probability for two random human beings to be two males?" and different if you ask "what is the probability for one random human being to be a male?". The second question has always probability 0.5, since it's a random human being.

The problem as it was stated was full of mistakes. Probably intentional, to confuse the readers and generate discussion. There is no trick at all, it is just bad mathematics.