Riddle for summer

We've been solving riddles for the past week at school, to help pass the time...Here is some to gear us into summer.

What is black when you buy it, red when you use it, and gray when you throw it away?

What word has three consecutive sets of double letters in it?


I am a three digit number.
My tens digit is five more than my ones digit.
My hundreds digit is eight less than my tens digit.
What number am I?

You throw away the outside. You then eat the outside and throw away the inside.

What did you eat?