Question

In 1978, a 200-gram sample of cobalt-60 was buried in the Yucca Mountains, just northwest of Las Vegas, Nevada. How much of this sample was present in 2004? The half-life of cobalt-60 is 5.23 years.

Answer 1

amount left = original amount * (1/2)^(total time ellapsed/length of half life), make sure the units for half life and time elapsed are the same (in this case, years)