Think about the answer from one angle. You have to think about it from another angle to verify it. I won't try it here. Hmm. How interesting
The first problem is that the touch ball is not put back. Touch number three for the third time. That's easy. . Actually, it's a lottery question. The answer must be 1/4.
I got the non-No.3 ball for the first time in another way. The probability of getting a non-No.3 ball for the second time is 2/3. The probability of getting the third ball is 1/2. Multiply three numbers to get 1/4 (this question is a typical lottery principle model).
The second question has been put back. . So the probability of touching every ball is the same every time.
Then analyze the questions, up to three. This means that at least one time it is 3. So it can be calculated that there is only one touch of 3, two touches of 3 and three touches of 3. The probability is (3 out of1) (1/4) * (3 out of 4) * (3 out of 2) (65433).
This is a binomial distribution of probability, and you can look it up, a typical probability model.
Another way of thinking. I didn't even touch 3 when I buckled it. . It's 1-(3/4) 3.
I don't understand. Hi. I
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I have to admit that LS helped me correct the wrong topic! I made a mistake, hehe. I won't change it. Look at LS.
But if you have time, you'd better look up several typical probability distribution models, which is very helpful to understand probability.
Classical probability Bernoulli experiment of quadratic distribution of geometric distribution Wait a minute.