Algebra-1

Question Analysis
This question tests the student's ability to apply the exponential function model to a real-world scenario. The key is to identify the initial population, the growth factor, and the number of periods.

Key Concept Explanation
The exponential function  () is used to model situations where the quantity changes by a constant factor over equal intervals of time.

Step-by-step Solution
1. Identify the initial mass grams.
2. Determine the decay factor (since the substance decays by 20% per year).
3. Identify the number of years

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