markpetefish markpetefish 29-04-2024 Mathematics Answered An unknown radioactive element decays into non-radioactive substances. In 800 days the radioactivity of a sample decreases by 35 percent. (a) What is the half-life of the element? half-life: (days) (b) How long will it take for a sample of 100 mg to decay to 63 mg? time needed: (days)