Question

how many positive three digit intigers contain at least one 3 as a digit but do not contain a 5 as a digit

Answer 1

you don't want 5 ? so forget about 5 while doing this problem -
assume there are only 9 digits

Answer 2

any ideas on how to approach this ? :)

Answer 3

maybe try this :
1) find total 3 digit integers that do not contain 5
2) find total 3 digit integers that do not contain 5 and 3
3) subtract