Question

the access code for a car's security system consists of four digits. the first digit cannot be 1 and the last digit must be even or zero. how many different codes are available?

Answer 1

For the 1st digit we can use 9 of them ( it cannot be 1 ). For the 2nd and the 3rd we can use 10 and for last one we can use 5 digits ( 0, 2 , 4 , 6 and 8 ).
9 · 10 · 10 · 5 = 4,500
Answer: 4.500 different codes.