Rosario is an ecologist who studies the change in the penguin population of Antarctica over time. The relationship between the elapsed time $t$, in years, since Rosario started studying the population, and the number of penguins, $P(t)$, is modeled by the following function: ###$P(t)=21{,}000\cdot \left(\dfrac{4}{7}\right)\^{\Large \frac{t}{3}}$ **Complete the following sentence about the rate of change in the penguin population.** The population of penguins loses $\dfrac{3}{7}$ of its size every [[☃ math-keypad 1]] years.