How long would it take a sample of this isotope to decay to just 68.18% of its original activity??HELP ME PLZ!

Question

The isotope 228-Ra has a half life of 1602 years. How long would it take a sample of this isotope to decay to just 68.18% of its original activity? Answer in years Error tolerance: ±1%

Can Anyone HELP ME PLZ!!!!!

Answer 1

k = 2.3Log2/t(1/2) = 0.693/t(1/2) = 0.693/1602 = 4.326 x 10^-4/yr

Log N1/N2 = kt/2.3

t = 2.3Log(100%/68.18%)/(4.326x10^-4) = (2.3)(0.1663)/(4.326x10^-4) = 884.1 yr