Answer:
The answer to the question is
50 % of the original amount of potassium 40 will be left after one half life or 1.25 billion years
Explanation:
To solve the question we note that the half life is the time for half of the quantity of substance that undergoes radioactive decay to disintegrate, thus
we have
half life of potassium 40 K₄₀ = 1.25 billion years
To support the believe tht the rock was formed 1.25 billion years ago we have
[tex]N_{(t)} =N_{(0)} (\frac{1}{2}) ^{\frac{t}{t_{\frac{1}{2} } } }[/tex]
After 1.25 billion years we have
[tex]N_{(t)} =N_{(0)} (\frac{1}{2}) ^{\frac{1.25billion}{1.25 billion} } } }[/tex] = [tex]N_{(t)} =N_{(0)} (\frac{1}{2}) ^{1 } } }[/tex] =0.5 of [tex]N_{(0)}[/tex] will be left or 50 % of the original amount of potassium 40 will be left
