a) 7!
= 7 . 6 . 5 . 4 . 3 . 2 . 1
= 5040
b) 3!.2!
= 3 . 2 . 1 . 2 . 1
= 6 . 2
= 12
c) 4!-2!
= 4 . 3 . 2 . 1 - 2 . 1
= 24 - 2
= 22
d) 0!/3!
= 1/(3 . 2 . 1)
= 1/6
