Question 1133045
Radium 221 has a half life of 30s.
 If a sample contains 96 units of radium 221, how much would remain after each time has elapsed?
: 
The radioactive decay formula: A = Ao*2^(-t/h), where
A = amt remaining after t time
Ao = initial amt (96 units)
t = time is seconds
h = half-life of substance (30s)
:
a) 30 seconds 
A = 96*2^(-30/30)
A = 96*2^-1
A = 96(1/2)
A = 48 units
:
b) 2 mins. that's 120 sec
A = 96*2^(-120/30)
A = 96*2^(-4), use your calc 
A = 96*.0625
A = 6 units after 2 min
:
c) 5mins, that's 300 sec
A = 96*2^(-300/30)
A = 96*2^(-10)
A = 96*.00975625
A =  .09375 units after 5 min