Half life story

I may have to send this one to overheard new york. I'm at the museum
of natural history. In the dinosaur room, I hear two sketchy looking
people standing in the corner. One of them is trying to explain the
concept of "half life":

It's like this. If you do drugs and say the half life of like coke is
10 days. That means after 10 days, half of the coke is cleared out of
your system. And then after another 10 days, another half is out. So
like technically after 20 days, 3/4 of the coke is out of your system.
You should wikidpedia it.