How many c-13 atoms are present, on average, in a 3.0000×104-atom sample of carbon?

316 atoms of C-13 There are three naturally occurring isotopes of carbon. C-12, C-13, and C-14. C-13 comprising 1.055% of the total carbon (on average). So to get the number of C-13 atoms in a sample of 3.0000x10^4 atoms, just multiply 3.0000 x 10^4 * 0.01055 = 316 atoms on average.