When does four plus four equal 9?

Answer 1

In standard arithmetic, four plus four equals 8. However, in certain mathematical systems, such as modular arithmetic, where numbers "wrap around" after reaching a certain value, four plus four can equal 9. This is because in modular arithmetic, numbers are considered congruent if they have the same remainder when divided by a specific number, known as the modulus.

Answer 2

When "plus" is defined in a non-standard way.