15x.18=2.7 50/2.7=18.519
Let me walk through mine here.
15ml bottle with 18 micro-grams of nicotine in it, so I put the micro-grams as .18 and multiplied by 15. This gives me 2.7 grams of nicotine per 15ml bottle.
The suggested toxic dose of nicotine is listed at 50 grams. I divided that by the 2.7 grams to get around 19 bottles.
Ah. I did not carry that out per pound. If I do, 475; 15ml bottles are needed to be toxic to a 25lbs child. 7,125 ml would be needed, or roughly 30; 8 oz (240ml) bottles.
I pay around $40 USD for a 240ml bottle of juice. To stand aside and watch a child of 25lbs kick back and chug away $40 of juice to me would seem rather terrible. A full 30 bottles like that would run $1,200 USD. Sorry, I know there are likely parents of human children who are stupid enough to let that happen. I just find it incredulous.
Again, if I'm off on my maths I'm sorry. I only took the government required general public education up to high school. No one ever really pushed STEM on me as it seemed clear I was just another bit of military fodder.
Now, I play catch up.
Your math is off:
A 15ml of 18mg contains 18mg nic per ml liquid. Therefore there's 270mg of nic in that single bottle.
mg == milligram not microgram