# In 1999 the worlds population reached 6 billion an was increasing at a rate of 1.3% per year. Assume that this growth rate remains constant, how do you write a formula for the world population (in billions) as a function of the number of years since 1999?

Jul 31, 2016

Population
$= 6 {\left(1 + 0.013\right)}^{n} b i l l i o n s$
Where $n$ is the number of $y e a r s$ since $1999$

#### Explanation:

Since 1.3% can be written as $0.013$
we can write the equation
Population
$= 6 {\left(1 + 0.013\right)}^{n} b i l l i o n s$
Where $n$ is the number of $y e a r s$ since $1999$
Assuming we want to know the population in the year $2016$
from the above equation $n$ that is the number of $y e a r s$ since $1999$
So
$n$
$= 2016 - 1999$
$= 17$ Years
Population in the $y e a r 2016$ as per the formula is
$= 6 {\left(1 + 0.013\right)}^{n} b i l l i o n s$
$= 6 {\left(1.013\right)}^{17} b i l l i o n s$
$= 6 \left(1.25\right) b i l l i o n s$
$= 7.5 b i l l i o n s$