(Direct Cost / (100, Desired Gross Profit)) * 100
Source: http://www.mrhvac.com/2011/10/26/how-to-calculate-the-selling-price-of-an-item/
I've never seen a comma placed like that in an equation. Why does it mean? Is it more commonly written in another way?
In fact, if you looked just further down they have calculated in an example that $100, 65 =35$ or $100-65=35$. So, in this context the command actually stands for a minus sign giving us $$\text { Selling price } = \frac {\text {Direct cost}}{100-\text {Desired gross profit}} \times 100$$
Personally, I have never seen this symbol used as a substitute for the minus sign. Hope it helps.