Question

Pd-100 has a half-life of 3.6 days. If one had 620,310,740 atoms at the

start, how many atoms would be present after 21.6 days?

Answer 1

Notice that 21.6 is 6 times the half-life of Pd-100, which means the amount of atoms is halved 6 times:

620,310,740 / 2^6 = 9,692,355.3125

so about 9,692,355 atoms remain.