If the half-life of carbon-14 is 6000 years, how many grams of carbon-14 should remain if a 72-gram sample sits around for 18,000 years?

Amount left = 9 g

Explanation:

Given data:

Half life of carbon-14 = 6000 years

Total amount = 72 g

Mass remain after 18000 years = ?

Solution:

Number of half lives = T elapsed / half life

Number of half lives = 18000 years / 6000 years

Number of half lives = 3

At time zero = 72 g

At first half life = 72 g/2 = 36 g

At second half life = 36 g/ 2= 18 g

At third half life = 18 g/2 = 9 g