[From the notes of Emily Moore, with modifications by Samuel A. Rebelsky.]
Using mathematical symbols to combine four fours it is possible to write expressions for all the numbers from 0 to 100, as well as millions of others. For example,
2 = 4/4 + 4/4.
3 = (4+4+4)/4.
64 = (4+4) * (4+4).
Using any symbols that do not themselves contain digits, see how many numbers you can form using four fours. Some should be easy. Some people find these numbers particularly difficult: 13, 19, 33, 85.