You can
put this solution on YOUR website!1st question is correct.
2nd question -- 3/28 is correct. The 2/7 is in there because after one book is chosen, you have two biology books out of seven total. You could also do (3C2)/(8C2) = 3/28.
3rd question is correct.
4th question -- If I told you "5 males and 2 females go out for pizza" can you figure out the probability?
5th question -- Use the same method as in the third question, 1 minus the probability of none of them are driving 60-70 mph.
6th question -- Coin tosses are independent, so P(tail) = 1/2.
7th question -- Now we have 13 girls and 11 boys, what is P(boy)?