The change represents a decay, and the percentage rate of decrease is 89%.
In Mathematics and Statistics, a population that increases at a specific period of time represent an exponential growth.
This ultimately implies that, a mathematical model for any population that increases by r percent per unit of time is an exponential function of this form:

Where:
- P(t ) represents the final population.
- t represents the time or number of years or days.
- I represents the initial population.
- r represents the growth rate.
Based on the exponential functions provided above, we can reasonably infer and logically deduce that the required exponential growth rate function is given by;

1 + r = 0.11
r = 0.11 - 1
r = -0.89 × 100
r = -89%