A new car costs $30,000, The value decreases by 15% each year. How do you find the car's value after 4 years?

1 Answer
Oct 19, 2015

After 4 years the car is worth $15,660.19

Explanation:

Let a_1=30,000 be the car's initial value, We knwo, that every year the new value can be calculated as:

a_{n+1}=a_n*(1-0.15)=0.85a_n

From this we know, that the consecutive values form a (decreasing) geometric sequence with: a_1=$30,000, q=0.85, and every term a_i (for i>=2) is the car's value after year number i-1, so the value we are looking for is a_5

a_5=a_1*q^(5-1)=a_1*q^4=30,000*(0.85)^4 ~~15,660.19