Advanced MathEasy–MediumTwo periods of exponential decay
Advanced Math practice question
A population is modelled by P(t) = 500(0.8)ᵗ, where t is the number of years from now. What is the population 2 years from now?
Answer: 320
P(2) = 500 × 0.8 × 0.8 = 500 × 0.64 = 320.
Common wrong answers
- If you answered 300
- 300 subtracts 20% of the ORIGINAL twice (100 + 100). In the second year the 20% is taken of 400, giving 80.
- If you answered 400
- 400 is P(1), after one year only.
- If you answered 800
- 800 is 500 × 1.6, adding 0.8 twice instead of multiplying.
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