Answer:
the answer maybe is 61.5 years (please check with others) tq
Step-by-step explanation:
40/2=20
20/2=10
10/2=5
5/2=2.5
2.5/2=1.25
so one half life is 12.3 years
then 12.3 ×5 =61 .5
(why 5 ? because it decay 5 times to get 1.25 from 20)
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