writing an equation that models exponential growth or decay

Question

There was a sample of 900

 milligrams of a radioactive substance to start a study. Since then, the sample has decayed by 5.2%

 each year.Let t

 be the number of years since the start of the study. Let y

 be the mass of the sample in milligrams.Write an exponential function showing the relationship between y

 and t

.

Answer 1

y= 900e^-.052t