posted by Taylor .
The radioactive element has a half-life of about 28 years and sometimes contaminates the soil. After 47 years, what percentage of a sample of the elements remain?
fraction remain = (1/2)^n where n is the number of half life
half life = p/n where p is the period of decaying i.e. 47 years
so, first find n (number of half life using the half life equation and then find the fraction remain. convert this fraction to %
hope that helps