Ahiker in africa discovers a skull that contains 21% of its original amount of c-14
( exponential decay )
find age of skull and round answer to nearest year

If the skull discovered by a hiker in Africa contains 21% of its original amount of C-14, the age of skull is 11, 689 years. This is calculated based from the fact that the half-life of c-14 is 5,730 years. So, in 5,730 years c-14 component on the skull is 50%; adding another 5,730 years makes c-14 component to 25%. Now, if it has 21% of c-14, we need to get 4% out from 5,730 years — resulting to 229 years.

In summary;

First half-life (50%): 5,730 years
Second half-life (25%): 5,730 years
Getting 4% of half-life to make it 21%: 229 years

Breakdown;
5,730 + 5,730 + 229 = 11, 689 years