Help please, I suck at permutations and combination.

1.) A. In how many different ways can a student answer a 20 question true-false examination?

B. In how many ways can he answer the examination if he is to answer 18 out of 20 questions?

2. In how many ways can 4 male students, 4 female students and a professor sit in a row for class picture if:

A. No restrictions?

B. the professor must be in the middle

C. a certain student and the professor must occupy the ends?

3. Find the number of ways of selecting 6 balls from 6 red balls, 3 green ball and 5 black balls if each selection consists of 2 red balls, 2 green balls and 2 black balls.

4. In how many ways can 13 people be grouped into two groups of 8 and 5 if a certain person is to be in the larger group?

5. Ten people is to sit a round table. Three particular people insist on sitting next to each other. In how many ways can ten be seated?

Help please, hope you can help me. Thank you very much.