How many years will it take for 88g tritium to decay to an 11g sample?

Answer 1

k = 0.693/t_1/2
Look up the value of half-life in your text or notes (or tables on the Internet).
Then ln(No/N) = kt
No = 88 g
N = 11 g
k = from above.
Solve for t.

Answer 2

Solve for t.