Nicotine mg/ml is... Total Nicotine divided by Total Milliliters.
You have 125ml of 36mg/ml. So each ml contains 36mg of Nicotine. The Total Nicotine is 125 x 36 => 4,500mg of Nicotine.
And your Total Milliliters is 125 + 250 => 375ml of volume.
So the mixture's mg/ml should be 4,500 / 375 => 12mg/ml
And since the PG to VG Ratio's are the same of what you Mixed with, the Mixture has the Same Ratio. 50/50
Does this make
sense?
Now do the Common
sense Double Check.
If I did equal parts of 36mg/ml with 0mg/ml it would cut the 36mg/ml in half. And I would have 18mg/ml.
But I didn't do equal parts. I Did 2 Parts 0mg/ml. So it should cut the 36mg/ml down by 1/3. Which would be 12mg/ml.
So it Passes the Common
sense Test.