cobalt-60 has a half-life of 5.26 years, how much of a 500 gram sample will be left after 21 years

500*'(1/2)^(21/5.26) grams

You have 14,000 atoms of radioisotope x, which has a half life of 1000 years how much of radioisotope x is after 9000 years ?

To determine how much of the 500 gram sample of cobalt-60 will be left after 21 years, we'll need to use the exponential decay formula:

N = N0 * (1/2)^(t / T)

where:
N = the remaining amount of the substance
N0 = the initial amount of the substance
t = the time (in this case, 21 years)
T = the half-life of the substance (in this case, 5.26 years)

Let's plug the values into the formula:

N = 500 * (1/2)^(21 / 5.26)

Now we can calculate the remaining amount of cobalt-60 after 21 years.