Question

There are only about 400,000 African elephants left in the world today. They are

classified as endangered by the International Union for Conservation of Nature, and
the population continues to decrease by 9% per year. What will the population of
African elephants be in fifty years?

Answer 1

In 50 years there'll be approximately 3582 elephants.

Explanation:

If they are decreasing at a rate of 9% per year, it means it's population by year is:

population(0) = 400000

population(1) = population(0)*(100% - 9%) = population(0)*(91%)

population(2) = population(1)*(91%) = population(0)*(91%)*(91%) = population(0)*(91%)²

population(3) = population(2)*(91%) = population(0)*(91%)²*(91%) = population(0)*(91%)³

And so on, so the number of population as years passes is:

population(n) = population(0)*(91/100)^n

In this case we want to know the population of elephants when n = 50, so we have:

population(50) = 400000*(0.91)^50 = 3582.033

In 50 years there'll be approximately 3582 elephants.