What number can you add to five and get four?

Question

No negatives, fractions, decimals, square roots, or equations.

Answer 1

5+(-1) is 5-1=4

Answer 2

5 is V in Roman numerals. 1 is I in Roman numerals.

I + V = IV or 4.

Technically the I is subtracted from the V but it looks like you added the I to the V to get IV.