I have 2, two part questions.

1. A box contains 3 yellow and 5 black balls. A ball is drawn and then replaced. This process is continued for a total of 5 draws. what is the probability of drawing:

a. exactly 4 black balls

b. at most 4 black balls

2. A test contains 20 multiple choice questions each with 3 choices. If a student guesses every answer, what is the probability he will get:

a. all the answers wrong

b. exactly 5 correct answers.

Thanks

~G