**Let's walk through a problem without the formula first just to make sure that we get the concept of half-life:**

**In 2000, you buried 15 kg of Carbon-14 in your backyard. Someone digs it up in the year 13,460. How much Carbon-14 did they find?**

**OK, That's 11,460 years (which is two half-lives...)**

**After 5730 years, there'd be 7.5 kg.**

**After 5730 more years, there'd be 3.75 kg.**

**Now, let's do one with the formula:**

**You discovered a new radioactive isotope and named it boogonium (don't ask). It's half life is 1.23 years. If you start with a sample of 45 grams, how much will be left in 6.7 years?**

**Plug this stuff in!**

**Grab a calculator!**

**YOUR TURN:**

**An alien radioactive isotope has a half-life of 238 years. If you start with a sample of 8 kg, how much will be left in 100 years?**