Question

C-14 has a half life if approximately 5700 years how many years will it take for the radioactivity of a sample to reach one-fourth of its original amount
A. 1425
B.5700
C.11400
D. 22800

Answer 1

This is an easy half-life problem.
Every half-life, a substance loses half its radioactivity.  So, after 2 half-lives, a substance will have a quarter of its radioactivity.
2 * 5,700 = 11,400 years
answer is C