A certain radioactive isotope decays exponentially. The table shows the mass , in grams, of a sample of this isotope after days. Which of the following statements is true about the function that models this relationship?
| t | M(t) |
|---|---|
| 0 | 100 |
| 2 | 81 |
| 4 | 65.61 |
The initial mass of the isotope was 100 grams, and it decreases by 20% every 2 days.
The initial mass of the isotope was 100 grams, and it decreases by 10% every day.
The initial mass of the isotope was 80 grams, and it decreases by 20% every 2 days.
The initial mass of the isotope was 80 grams, and it decreases by 10% every day.
