Question

Radium-226 has a half-life of 1620 years. for a 150 gram sample, how many grams will remain after 200 years?

Answer 1

Ah, yes

if you start with P amount of something and the half life is h units (in years) and the time elapsed is t (in years) then the amount left is A

the equation is
$A=P(\frac{1}{2})^\frac{t}{h}$


so
given
h=1620
P=150
t=200
so
$A=150(\frac{1}{2})^\frac{200}{1620}$
$A=150(\frac{1}{2})^\frac{10}{81}$
use your calculator
A≈137.69781917515g
about 138grams left