We have been given that last month Maria purchased a new cell phone for $500. The store manager told her that her cell phone would depreciate by 70% every 6 months.
We know that an exponential function is in form
, where,
y = Final value,
a = Initial value,
r = Decay rate in decimal form,
x = Time in years.
Let us convert
into decimal form.

Initial value of car is 500, so
.
Since value of phone depreciates every months, so value of phone will depreciate twice in a year.
Upon substituting our given values in exponential decay function, we will get:

To find the value of phone after 2 years, we will substitute
in our equation.


Therefore, option D is the correct choice.
Let us simplify our equation.

Therefore, option B is correct as well.