Half-life help please?

Question

The half-life of carbon-14 is 5700 years. A fossil was found to contain only 70% of its original 50 g of carbon-14. Approx. how old is the fossil?

Any help would be appreciated. I used to be able to do this easily but need a refresher as I haven't in a while. Please explain as completely as possible so I fully understand and can do similar problems on my own. Thanks so much and 10 points to a best answer!

Answer 1

well the formula might help

there are different 'versions' of it, but I write it like this:

A(t) = 1/2*x ^t/half-life

so plug in the numbers

50 = 1/2 x ^ .70/5700

solve.