i think 100 IS a magic number here.

Percentage is vastly used, but also per mille (1/1000) is often used, and basis point (1/10.000) and percentmille (1/100.000) are used enought to have their own name.

I would change you function to getPerPart(value, part) and getFromPart(value, part), maybe with a default getPerPart(value) and getFromPart(value) witch use DEFAULT_PART_VALUE = 100

also you may still want to write a getPercent, in that case the use of hardcoded 100 is fine

I think 100 IS a magic number here.

Percentage is vastly used, but also per mille (1/1000) is often used, and basis point (1/10.000) and percent mille (1/100.000) are used enough to have their own name.

I would change your function to getPerPart(value, part) and getFromPart(value, part), maybe with a default getPerPart(value) and getFromPart(value), which use DEFAULT_PART_VALUE = 100.

Also, you may still want to write a getPercent, in which case the use of hardcoded 100 is fine.