The first question, in the case of taking the red ball for the first time, take the second ball from the remaining four red balls, two white balls and six balls. According to the classical probability calculation, the probability of getting the red ball is 4/6.
The probability of getting the red ball at the same time for the first time and the second time is (5X4)/(7X6).
The second question is even number 24681012141618 20 22 24 26 28 30 * *15. Choose 10 from this 15 and 10 from 30.
I won't ask your classmates if I haven't reviewed the distribution function of the third question. I also want to take the final exam. I hope I won't fail. Let's go