Where can I find the formula that determines how much water to add if I have to make 100 gr Isopropylalkohol 50 °?

I think one speaks rather of% than of degrees. 50% is 50% V/V This dilution is prepared by diluting 42.5 g isopropanol to 100g. Isopropanol distinguishes itself from ethanol by the fact that the product is 100%. For ethanol 94 to 96 °.