3.39: Password counting with letters, digits and symbols
A 6-character password is formed from letters A–D, numbers 1–4 and symbols , , , . No character may be used more than once.
(a)(i)[1]
Find the number of different 6-character passwords that can be formed.
(a)(ii)[1]
How many of these end with a symbol?
(b)[2]
Find how many include all four symbols, but do not start or end with a symbol.