Is this math correct?
If I have 15 lbs or 3 parts at 1.162 and add 5 lbs or 1 part at 1.020 would the new gravity be 1.127?
3 X 1.162 + 1 X 1.020 / 4 = 1.127, it just doesn't seem right.
Except for missing parentheses, looks right to me: (3 X 1.162 + 1 X 1.020) / 4 = 1.127. I think that you are thinking about it the correct way.