How do you get the equation

Question

In 2002

, a sample of a radioactive substance had a mass of 550

 milligrams. Since then, the sample has decayed by 9.3%

 each year.Let t

 be the number of years since 2002

. Let y

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

 and t

. 

Answer 1

y=550(1-.093)^t

y=550(.907)^t