science
posted by chuck on .
The halflife of carbon 14 is 5730 years. if a 1 g sample of old carbon is 1/8 as radioactive as 1 g of a current sample, then the age of the old sample is about ___________years.
22,900
17,200
11,500
716

if I am correct, B. 17,200. I looked it up and this is what it said "b.) 17,200
if it takes 5730 years to be half then it takes 2*5730 years to be a quarter and 3*5730 years to be an eighth (2^3=8) so to get an 1/8 you need to half it 3 times and it takes 5730 years to half each time, thus 3*5730 ~ 17,200" 
Thanks

No problem.