Advanced MathMediumDecay rate from an exponential model
Advanced Math practice question
The value of a car, in dollars, t years after it is bought is modelled by V(t) = 12,000(0.85)ᵗ. By what percent does the car's value decrease each year, according to the model?
Answer: 15
Each year the value is multiplied by 0.85, so it keeps 85% of its value and loses 100% − 85% = 15%.
Common wrong answers
- If you answered 85
- 85% is the fraction of the value that REMAINS each year, not the decrease.
- If you answered 1800
- 1,800 is 15% of 12,000, the dollar loss in the FIRST year only. The question asks for the percent.
- If you answered 0.85
- 0.85 is the decay factor. The percent decrease is 1 − 0.85 = 0.15 = 15%.
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