If command to do math.

So I am having an issues trying to get my spreadsheet to do some math for me. I need to get a command if it is not an if command. To do some math for me so I am not getting data wrong and not have to correct it by hand. I have a Value being totaled into a column. Call it G2. I have a (triggering value =Yes) in cell lets call it D2, that would cause G2 to be divided by a static number say 50. This calculation would then give the result without having to always go in and not have to change it if the value is not Yes in D2.  Hopefully this makes sense. In the long run I have values added up to 1 cell then trying to get it to divide by a number if the answer to one question is yes.