There are 25 machinists employeed by a company

a. if a night crew consists of 3 machinists, how many different crews are possible.

(is this a combination of 25,3?)

b. if the machinists are ranked 1 (best) - 25 (worst) how many of these crews of 3 would not have the best machinist?

i tried a combination of 24, 2 but i don't think that's right

c. how many of the crews of 3 would have at least 1 of the top 10 best machinists

i tried another combinatino but i don't think this is right cuz i got a smaller # than B

d. if one of these crews is selected at random, what is the probability that worst machinist will not work that night?