Radioactive carbon decays exponentially with a half-life of 5,780 years. Determine how long ago a sample of carbon began to decay if there is now 5% of it left.

I'm not sure how to get started to all help is appreciated!

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- Dec 10th 2009, 07:14 PMAlice96Half-Life calculation
Radioactive carbon decays exponentially with a half-life of 5,780 years. Determine how long ago a sample of carbon began to decay if there is now 5% of it left.

I'm not sure how to get started to all help is appreciated! - Dec 10th 2009, 07:24 PMpickslides
Let A= the amount of radioactive material remaining at anytime t, you have the following information

Use the following $\displaystyle A = A_0e^{kt}$

at $\displaystyle t=0, A = A_0$ and $\displaystyle t=5780, A = \frac{A_0}{2}$

this will help you solve for k.

After this solve for t when $\displaystyle A = 0.05\times A_0$