Tritium (half-life = 12.3 y) is used to verify the age of expensive brandies. If an old brandy contains only the following fraction of the tritium present in new brandy, how long ago was it produced?

Question

1/128

Answer 1

After one half life the ratio is 1/2
After two half lives the ratio is 1/4
After three the ratio is 1/8

so how many half lives to get to 1/128?

Answer 2

24.6