SOLUTION: The price of a used car is decreasing exponentially. Today it is worth %15,000. In 3 months from now, it will only be worth $14,000. How much was it worth a year ago?

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Question 1131523: The price of a used car is decreasing exponentially. Today it is worth %15,000. In 3 months from now, it will only be worth $14,000. How much was it worth a year ago?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Find the monthly rate of loss
+14000+=+15000%2A%28+1+-+r+%29%5E3+
+14%2F15+=+%28+1+-+r+%29%5E3+
+log%28+14%2F15+%29+=3%2Alog%28+1+-+r+%29+
+log%28+.9333+%29+=+3%2Alog%28+1+-+r+%29+
+-.029963%2F3+=+log%28+1+-+r+%29+
+-.0099877+=+log%28+1+-+r+%29+
+1+-+r+=+.977265+
+r+=+.0227+ monthly rate of loss
-------------------------------------------
1 yr ago, or 12 months ago compared to today:
+15000+=+C%2A%28+1+-+.0227+%29%5E12%0D%0A%7B%7B%7B+15000+=+C%2A.9773%5E12+
+15000+=+C%2A.75916+
+C+=+19758.61+
A year ago the value was $19,758.61
check the math, get another opinion