6

Set 4: Exponential Functions (Intermediate)

Explanation

Answer: A

A car's value depreciates exponentially. The table shows its value over three years. What is the annual depreciation rate?

YearValue ($)
030,000
124,000
219,200
A.

20%

✓ Correct
B.

80%

C.

24%

D.

6%

Detailed Explanation

Choice A is correct. Choice A is the correct answer. Find the decay factor and convert to a rate. 1. Decay Factor: b=24,00030,000=0.8b = \frac{24,000}{30,000} = 0.8. 2. Verify: 19,20024,000=0.8\frac{19,200}{24,000} = 0.8 (consistent). 3. Depreciation Rate: r=1b=10.8=0.2=20%r = 1 - b = 1 - 0.8 = 0.2 = 20\%. Strategic Tip: Depreciation rate = 1(decay factor)1- \text{(decay factor)}. If the value keeps 80%, it loses 20%. Choice B is incorrect because 80% is the retention rate (what remains), not the depreciation rate. Choice C is incorrect because this is the dollar amount lost in year 1, not the percentage rate. Choice D is incorrect because this doesn't match the pattern in the table.

Key Steps:

The correct answer is 20%

Why others are wrong:
B: Choice B is incorrect and may result from a calculation error.
C: Choice C is incorrect and may result from a calculation error.
D: Choice D is incorrect and may result from a calculation error.

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