Question

To use a certain cash machine, you ned a persona identification code. If each code consists of two letters followed by one of the digits from 1-9(such as AQ7 or BB3) or one letter followed by two difits (such as Q3 or J88), how many different codes can be assigned?

I think there are 9 numbers but my teacher said I have to use 10?

Answer 1

Well, there are 9 digits from 1-9, not 10, that would include the 0

I will also assume that letters and numbers may be repeated.

case1 , 2 letters followed by a number
number of ways = 26x26x9 = 6048
case 2, 1 letter followed by 2 numbers
number of ways = 26x9x9 = 2106

total = 8154

of no digits or letters may be repeated, the number of ways would be
26x25x9 + 9x8x26
= ....

Answer 2

Oh ok. I think numbers and letters can be repeated, but thank you for clearing up the amount of numbers.