a+B = 1/ 15+2/ 15 = 3/ 15 = 1/5
2, the probability of the first white ball is 2/6= 1/3, and the probability of the second white ball is 4/6X2/5=4/ 15.
The probability of the third white ball is 4/6X3/5X2/4= 1/5, so n is 3. "Remember, every time you take a ball, you lose one, and the denominator is of course reduced by one; If you take it out and put it back, the denominator is still the same. "
Please invite a round of "2523487500" to nearly one million "This is my Baidu. I hope you can tell me when you know the answer. I am curious about how to understand this English sentence. "