Carbon 14 is radioactive material with 5700 year of half-time which will change it into carbon-12, a more stable substance. If the age of the fossil is 11,400 years old, then the amount of half-time passed would be: 11,400 years/ (5,700years/ half-time)= 2 half-time.
Since it undergo 2 half-time, the percentage should be: 100% * (1/2)^2= 25%
