Scrabble is a word game where players create words from random letters. To start, players choose a simple random sample of seven letters from a population of 100 tiles. Consider the first draw of seven letters.

1. How many groups of seven letters are possible? Leave an answer in simplified faction form.

2. How many possible groups of all vowels (A, E, I, O, U) are possible? Leave an answer in simplified faction form.

3. What is the probability that the draw will contain only letters? Leave an answer in simplified faction form.