It's not an integer because integers must be positive in order to be rational integers. It can still be considered an integer in some cases, but typically you dount count numbers using negatives, do you?
The cookie was 51 cent beacsue they 13 quarters add up to $4 and then he but a drink for 13 cent. add that and you get $4.39 then you subtract that from. the $4.90
