Roman Subtraction

I had a fight with my dad on the dinner table over my sister’s 4th grade math homework - how did the Romans subtract?

For him it kinda looked like:

   V
- IV
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But that is just shows how ingrained the method of decimal mathematics is that we can’t even think of the Roman way of subtraction. My sister’s book shows the following steps:

V - IV = 5 - 4 = 1 = I

That’s actually pretty dumb right, I mean why teach them Roman numerals if you are going to fall back into the decimal way of doing things.

Not just her textbook but like a lot of these websites:

Example 1, Example 2, Example 3, …

I actually ended up finding the actual answer as well: Calculating With Roman Numerals is Not So Difficult, How Did the Romans Calculate?, Arithmetic with Roman Numerals, Arithmetical Calculation with Roman Numerals and the Abacus, Roman Numerals and Arithmetic, How to Add and Subtract Roman Numerals, How Did Anyone Do Math in Roman Numerals?, Code Example

no point in writing this now.