wikiHow Calculating Half-Life Practice Problems 1. A radioactive substance has a decay constant of 0.02 per year. Calculate its half-life. 2. The half-life of a radioactive isotope is 5 days. Calculate its decay constant. 3. A sample of a radioactive material initially contains 1000 atoms. After 1 hour, only 500 atoms remain. What is the half-life of this material? 4. A radioactive substance has a half-life of 10 minutes. If you start with 200 grams, how much will remain after 30 minutes? 5. The decay constant of a radioactive substance is 0.05 per day. Calculate its half-life. 6. A sample of radioactive material decays to 1/8 of its original activity in 24 hours. What is its half-life? 7. If the half-life of a radioactive element is 2 years, how long will it take for 1/16 of the initial amount to remain? 8. A radioactive substance has a half-life of 3 hours. If you start with 1000 atoms, how many will remain after 9 hours? 9. The decay constant of a radioactive isotope is 0.1 per minute. Calculate its half-life. 10. A sample of radioactive material has an initial mass of 500 grams. If its half-life is 7 days, what will be its mass after 21 days? 11. A radioactive substance decays to 1/4 of its original amount in 30 minutes. What is its half-life? 12. The half-life of a radioactive element is 1 year. How long will it take for the initial amount to decrease to 1/8? 13. A sample of radioactive material has a half-life of 2 hours. If you start with 800 grams, how much will remain after 6 hours? 14. The decay constant of a radioactive substance is 0.03 per day. Calculate its half-life. 15. A radioactive isotope has a half-life of 15 minutes. If you start with 2000 atoms, how many will remain after 1 hour? 16. A sample of a radioactive material decays to 1/10 of its original amount in 40 minutes. What is its half-life? 17. If the half-life of a radioactive element is 5 years, how long will it take for 1/32 of the initial amount to remain? 18. A radioactive substance has a half-life of 6 hours. If you start with 500 atoms, how many will remain after 18 hours? 19. The decay constant of a radioactive isotope is 0.05 per minute. Calculate its half-life. 20. A sample of radioactive material has an initial mass of 100 grams. If its half-life is 10 days, what will be its mass after 30 days? Page