chemistry
posted by bob .
Strontium90 has halflife of 28 years. if a 1.00mg sample was stored for 112 years. what mass of Sr90 would remain?

k = 0.693/t_{1/2}
Substitute k in the following:
ln(No/N) = kt
No = 1 mg
N = mg remaining after t time
k from above.
t = 112 years.