The half-life of carbon-14 is about 5700 years.

Question

You find a piece of cloth painted with organic dye. By analyzing the dye, you find that only 76% of the carbon-14 originally in the dye remains. When was the cloth painted?

Answer 1

(1/2)^(t/5700) = 0.76
t = 5700 * ln0.76/ln0.5 = 2257 years ago