The different ways in which numbers slide up, down, sideways, diagonally.

Is the example in the post part of the fifth type of arithmetic?

1. Addition +
2. Subtraction -
3. Multiplication x
4. Division /
5. Modulo %

The first time I learned about modulo as its' own branch of arithmetic was long out of school already, I had only hazily heard of it, on a PBS Nova documentary in the 1990s about Fermat's famous theorem and when it was proven after centuries of failed tries.

I think it's ambiguous and the 90% actually makes more sense. If you increase something by 5m you are taking the original value and adding 5m to it. For multiplication you should probably avoid the word increase and say scaled by instead. 10% scaled by 180% is 18%.