Thorium -228 is a radioactive substance that decays 50% every 1.9 years. how much of a 50 gram sample will exist after 22.8 years? round to 3 decimal places. use the formula a=a0e^ -kt.
a.) 19.34 grams
b.) 30.32 grams
c.) 0.124 grams
d.) 12.4 grams
e.) 7.48 grams

Step-by-step explanation:

The exponential decrease formula that we must use is:

Where A is the amount of thorium as a function of time

is the initial amount and k is the decrease rate

We know that initially there are 50 gr and that you decay 50% every 1.9 years.

So

We solve the equation for k

After 22.8 years the amount of thorium that exists is: