At the end of three half lives, we will have about 25 g of potassium-40 left.
What is half life?
The term half life refers to the time taken fro half of the amount of the radioactive atoms to remain. We know that; k = 0.693/t1/2
Where t1/2 = 1.28x10^9 years
k = 0.693/ 1.28x10^9 years = 5.4 * 10^-10 year-1
Using;
N(t) = Noe^-kt
N(t) = 200e^-(5.4 * 10^-10 * 3.84 * 10^9)
N(t) = 25 g
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