Question

how many four digit numbers can be formed using the digits 0,1,2,3,4 and 5 if repitation of digits is allowed?​

Answer 1

For positive 4 digit numbers: the first, second and third digits can be any one of the digits 1-5. To be even, the last digit must be 2 or 4. So the total number of positive 4 digit numbers that qualify is 5*5*5*2, or 250.

For each of these there is a corresponding negative 4 digit number. So the total is 2*250, or 500.