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

EDIT: thanks to Janes cognizance. I fix. See later post.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

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