Question

Carbon-14 has a half life of 5,730 years.after how many half-life will 120 grams of carbon-14 decay to 15 grams?

Answer 1

There's a pretty helpful equation that can help you solve this.
A=Ao(.5)^(t/h)
In this equation, A is the final amount, Ao is the initial amount, t is the time, and h is the half life. So if you plug all that in, you get
15=120(1/2)^(t/5730)
Now all you have to do is solve for t.