Question

A fossilized leaf contains 24% of its normal amount of carbon 14. how old is the fossil (to the nearest year)? use 5600 years as the half-life of carbon 14.

Answer 1

The Half life is the time taken for a radioisotope or a radioactive substance to decay by half its original amount. The half life of carbon 14 is 5600 years. 
Original mass is 100%
Remaining amount is 24% 
Therefore; 0.24 = 1 × (1/2)^n
                     n = log 0.24/log 0.5
                        = 2.06
therefore, the age of the fossil is 5600×2.06
 = 11529.8 
 ≈ 11529 years