Permutations are formed using all the digits 1,2,3...,9 without repetition.

Determine the number of permutations if:

a) the digits 1,2,3 are together but not necessarily in their natural order

b) even and odd digits alternate

c) the first is an odd digit and the last is on of 1,2,3,4

My thinking for

a) 1,2,3 are together which is 3! and the rest is 6 numbers which is 6! so 3!*6!=4320