Question

The access code for a cars security system consist of four digits the first digit cannot be 1 and the last digit must be odd how many different codes are avaiable

Answer 1

So we have 10 numbers 0 - 9 
0 1 2 3 4 5 6 7 8 9 
The first digit cannot be 1
therefore there are 9 possibilities 
0 2 3 4 5 6 7 8 9 

digits 2 and 3 can be numbers 0 through 9
therefore there are 10 possibilities for digits 2 and 3 
digits 2 and 3 are a total of 2 digits
and the last digit must be odd so there are 5 possibilities -> 1 3 5 7 9 
so 
$9 * 10^2 * 5 => 9 * 100 * 5 => 45* 100 = 45,000$
 codes available