Algebra-1

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

Key Concept Explanation
The exponential function  () is used to model situations where the quantity decreases by a constant factor over equal intervals of time. In this case, the mass of the radioactive substance decays by 20% per year.

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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