WOW! I got lightheaded just reading this.
Let me give it a shot. Hoosier hooked me up when I first got started, maybe I can return the favor somewhat
You have 10ml of 24mg nic and want X amount of 18mg.
10ml of 24mg nicotine is 240mg of nic.
Now if you work it backwards, 240mg of nic ÷ 24mg strength = 10ml, which is what you have now.
But you want 18mg.
240mg ÷ 18mg = 13.3333333333333 ml.
Since you already have 10ml, you need 3.33ml of 0mg *something* to cut your
juice to 18mg so you have to add 3.33ml of something to get your strength where you want it.
Now we're using 18% flavoring.
3.33 * 0.18 = 0.5994 (let's say 0.6 just for fun).
and
3.33 - 0.6 = 2.73
So to get to 18mg, you need -
1. The 10ml you already have
2. 2.73ml of 0mg something, and
3. 0.6mg of flavoring.
My numbers are a tiny bit different than Hoosier's and I think we can all see why, but either way will work just fine.