Question

Atoms of element A decay to atoms of element B with a half-life of 20,000 years. If there are 10,000 atoms of A to begin with (and 0 atoms of B), how long will it take for there to be 2,500 atoms of A?

Answer 1

         atoms    10000         5000      2500

         Half life      0                1              2


From the above description, we have 2500 atoms left after 2 half lives.

=  2 * 20000 =  40000

That is after 40000 years.

Answer 2

Answer: the answer is B

Explanation: