The probability of throwing a coin once is positive, it is half. Similarly, the probability of throwing a coin at random is negative and half.
The law of addition: the probability that a coin is tossed heads or tails is 1. The conjunction used here is "or", which is equivalent to the addition of two halves and the sum is equal to 1. This is the law of addition.
Law of Multiplication: Coins are tossed twice in a row, and the probability that the first and second times are heads is one in four. The conjunction used here is "and", so multiplication is necessary. Because throwing once is positive, it does not affect the result of throwing the second time. These two times do not interfere with each other, so multiplication is necessary.
Let's use the genetic problem again. Suppose there is a couple now. Their chances of having children are half that of their daughters and half that of their sons.
So if you ask, what is the probability that the couple will have two children in a row, the first child will have a son and the second child will have a daughter? It's connected by "sum" here, so by multiplication, the answer is a quarter.
If one spouse is an albino aa and the other spouse is a carrier Aa, then the probability of giving birth to an albino child is half.
Q: What are the chances that they have an albino daughter?
Because the probability of albinism is half, and the probability of having a daughter is half, we should use "and" to connect here, so we use multiplication. The answer is a quarter.
To sum up, this kind of problem is to find conjunctions, multiplication is "sum" and addition is "or"
-The first-line teacher from the "Life Science" team in Senior Three, I hope to help you.