Annapurna C. answered • 03/14/19

PhD Tutor

Radioactive decays are first order reactions

ln(At/Ao) = -kt

Ao = 100g, t = 8 days, At = 60 g , Substitute and find k value

Now, with this value of k use the equation again, this time to find t

Ao = 100g, At = 25g, k we found, substitute and find t