SOLUTION: A certain car depreciates about 15% each year. The original value of the car is $20,000 what is the function for this and how long will it take for the value of the car to reach 10

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Question 1113453: A certain car depreciates about 15% each year. The original value of the car is $20,000 what is the function for this and how long will it take for the value of the car to reach 10,000
Answer by josgarithmetic(39616) About Me  (Show Source):
You can put this solution on YOUR website!
100-15=85
Keeps 85% each year

20000%280.85%29%5Ex=10000
2%280.85%29%5Ex=1
0.85%5Ex=1%2F2
log%28%280.85%5Ex%29%29=log%28%281%2F2%29%29
x=log%28%281%2F2%29%29%2Flog%28%280.85%29%29
x=4.265

4 years 3 months
(maybe slightly more)