A radioactive isotope has a half-life of 9 hours. How do you find the amount of the isotope left from a 80-milligram sample after 54 hours?
After 54 hours, 1.25 milligrams of the sample will be left.
After a half-life period, the quantity of the sample with be reduced to half.
So, after 9 hours, amount of sample left
After another 9 hours, amount of sample left
Do you see the pattern emerging?
In 54 hours, there are
Therefore, amount of sample left after 54 hours
= amount of sample left after 6 half-life periods