[abcs12000]

وعليكم السلام ورحمة الله وبركاته
الحل
a=a0*exp(-L*t

first a0 =1200
a=150
t=100min
now substitute
we get the following
150=1200exp(-L*100

calculate L we find
L=(Ln(8))/100
L=.021/min

this is the decay const.
from this constant now we can find out the half life
L=Ln2/ t half
0.021=0.693/ t half
t half (half life )=33min
33 دقيقه