1. A certain radioactive substance has a half-life of 1200 years. If a sample of the substance is 1000 grams, how much of the substance will be left in 10,000 years?

2. The half-life of uranium-235 is approximately 710,000,000 years. Of a 10-gram sample,
how much will remain after 2000 years?

3. A radioactive element has a half-life of 6,525 years. How much of a 70 gram block will be left after 5,000 years?

4. What is the half-life of a radioactive element that weighed 40 grams in 1900 but only weighed 37 grams in 2005?

5. The population of Logtown is growing at 7.2% per decade. If the population is 45,000 in 2004, predict the population in 2039.

6. Susan invests $4000 in a retirement fund when she is 25, expecting to retire when she is 55. If the fund pays 6% interest, compounded quarterly (every 3 months), how much will she have when she retires? John decides to wait and save his money. When he is 45, he has $15000 to invest in the same fund. How much does he have when he retires?

7. The population of Mathville was 20,000 in 1970 and is growing at 2.3% per year. If the population is growing exponentially, what will the population be in the year 2020?

8. $8, 000 is invested in an account at an annual rate of 6% interest
compounded continuously.
i. How long will it take for the account to double?
ii. When will you have $30, 000?
iii. How much will you have after 2 years?