2.7: 5-digit codes with digit restrictions
A 5-digit code is to be formed from the digits 1, 2, 3, 4, 5, 6, 7, 8, 9. Each digit can be used once only in any code.
(i)[2]
Find how many codes can be formed if the first digit of the code is 6 and the other four digits are odd.
(ii)[2]
Find how many codes can be formed if each of the first three digits is even.
(iii)[2]
Find how many codes can be formed if the first and last digits are prime.