half life means exactly 1/2 of what's left decays
example
if yo has 16grams
if half life is 1 hour, after 1 hour, 8g is left
after another hour, 4g is left
after another your, 2g is left
etc
so find how many half lifes have elapes
so
the amount left after n halflives when you start with P amount is
A=P(1/2)^n
5hr=60*5=300mins
300/30=10
10 half lifves
P=1500
n=10
A=1500(1/2)^10
A=375/256
A≈1.46484g
about 1.5g left
