A hint to get started
Count possible phone numbers before excluding the correct one
A girl wishes to phone a friend but cannot remember the exact number. She knows that it is a five-digit number, that it is even, and that it consists of the digits 2, 3, 4, 5 and 6 in some order. Using this information, find the largest number of different wrong telephone numbers she could try.
[2002/I/17(b)]
CJC · Discussion · Question 2
Start with the even final digit.