chemistry
posted by Urgent Help .
Strontium90 decays through the emission of beta particles. It has a halflife of 29 years. How long does it take for 80% of a sample of strontium90 to decay?
Show process of how you got this

k = 0.693/t_{1/2}
ln(No/N) = kt
Use No = 100
N = 20
k from above
solve for t in years.