Probability with letter permutations!

13. Suppose a bag contains the letters to spell

probability.

a) How many four-letter arrangements are

possible using these letters?

I made 4 separate cases (no double letters, i doubles, b doubles, both b and i doubles) and added them to get 3074 ways. Dunno if this is correct

b) What is the probability that Barb

chooses four letters from the bag in the

order that spell her name?

2/3074

d) What four-letter arrangement would be

most likely to be picked? Explain your

reasoning.

One containing at least one i and b.

Can anyone tell me if i did this correctly, the solutions does not have the answer for this question.