A fossil was found to have 1/4 the number of Carbon 14 atoms present then when the animal died. The half life for carbon 14 is 5730 years. How old is the fossil?

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Originally Posted by teacherjenn4

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I am a parent trying to help my High school freshman daughter solve this problem but I am clueless. I don't just want the answer but if you show me how you got the answer I think I can explain it to her better.

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Originally Posted by teacherjenn4

show us your attempt at solving the problem and then we will help you.

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5730 + 2865 = 8595 Would this answer be right?

Ah, no, not quite right.

Half life has a special behaviour. Say something has a half life of 10 minutes and there is initially 128 kg of that thing.

After 10 min, there would be 128/2 = 64 kg
After 20 min, there would be 64/2 = 32 kg
After 30 min, there would be 32/2 = 16 kg
After 40 min, there would be 16/2 = 8 kg
After 50 min, there would be 8/2 = 4 kg

And so on.

So, in your question,
At the time of death, there were x number of C-14 atoms.
After 5730 years, there would be x/2 number of C-14 atoms.
After (5730*2) years, there would be (x/2)/2 number of C-14 atoms.

Does it make sense?

This is half life. It means the amount/mass halves for each half life period.

5730 x 2 = 11460 Is this correct

Right :)