A sample holds 400 grams of carbon-14. About how much is left after 11,460 years?

1. A half-life is the time in which an exponentially decaying quantity falls to half of what it was. 2. Carbon-14 has a half-life of 5,730 years. 3. Divide the elapsed time by the half-life to count how many halvings have happened. 4. That gives 11,460 divided by 5,730, which is exactly 2. 5. So the sample halves twice over. 6. The first halving takes 400 grams down to 200 grams. 7. The second halving takes 200 grams down to 100 grams. 8. About 200 grams counts only one halving and stops halfway through the elapsed time. 9. About 300 grams subtracts a quarter each time rather than halving. 10. About 400 grams treats the starting amount as unchanged, which no decay model allows. _Source: OpenStax Precalculus (CC BY 4.0), section 4.7 Exponential and Logarithmic Models_