Answer:
By 2020, there will be 1,147 species of birds left
Step-by-step explanation:
The general model for an exponential decrease is;
y = I(1 - r)^t
where in this case;
y is the number of bird species at a particular decade from the initial
I is the number of birds initially at 1990
r is the decrease percentage which is 1.5% per decade ; 1.5% = 1.5/100 = 0.015
t in this case will be the number of decades after the initial
Mathematically, a decade is 10 years
The difference between 2020 and 1990 is 30
The number of decades in 30 years is 30/10 = 3
so t will be 3 here
Substituting these values into the equation, we have
y = 1200(1-0.015)^3
y = 1200(0.985)^3 = 1,146.8
To the nearest whole number, this is 1,147
