Question

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?
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