Hallo,
I counted 5 minus 0.5 but the result wasn’t 4.5

then this is workflow work
Is this my wrong workflow or the system?
It’s because the field in which you are displaying the result is a text field. If it was an input field with a Content format of Decimal, it would just work. If you want to use a text field, you have to add :formatted as or :rounded to to the end of the formula.
Best…
Mike