An unknown radioactive element decays into non-radioactive substances. In 160 days the radioactivity of a sample decreases by 61 percent.

Question

(a) What is the half-life of the element? 

half-life:    

(b) How long will it take for a sample of 100 mg to decay to 70 mg? 

time needed:   

Answer 1

0.39 = e^160k

Determine value of k.

0.5 = e^kt, use value of k from above and solve for t