Please check my answers, if any of these is not correct, please help. Thank you very much.

Three marbles are drawn at random from an urn containing 8 black, 7 white, and 5 red marbles.

What is the probability that none of them are white. Answer: .

What is the probability that at least one of them is red? Answer:

A drawer contains 8 blue socks, 4 green socks, and 6 brown socks. If you choose 2 socks at random, what is the probability that they are both brown? Answer:

On a 10-questions true-false test, the questions are answered at random. What is the probability of answering at least 8 questions correctly? Answer:

Three letters are chosen at random from the word POSTER. What is the probability that the selection will contain E or O or both?

Please help me with this one.