Here's an interesting puzzle:
Using only the number 4 and any mathematical symbols you like, make every number from 1 to 100. For example to make "1", I would do 4/4.
Some more rules:
1. combining 4s is legal. E.g., "44" is valid.
2. Although you could just add 4/4 (aka 1) as many times as you needed to get to a particular number, that's kind of a cop out.