Question

The initial amount of radioactive substance is 52 grams. The substance decays at a rate of 1%. After 12 years, how many grams of the substance is present? Approximate to the nearest gram.

Answer 1

If the rate of decay is 1% per year, the number of grams present after 12 years is found from:
$52\times(0.99)^{12}=46\ grams$
An alternative solution can use the following equation:
$N(t)= N_{0} e^{-\lambda t}$
Plugging in given values, we get:
$N=52\times e^{-0.01\times t}=46\ grams$