Question

Apply the problem-solving techniques to solve the following

problem.
Population decrease In 1990, a rural area had 1200 bird
species. If species of birds are becoming extinct at the rate of
1.5% per decade (10 years), how many bird species will there be
left in the
year
2020?

Answer 1

By 2020, there will be 1,147 species of birds left

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