8 million (8 x 106)can be entered into your calculator as 8E6

8 and then 2nd function EE

Calculating population growth N =No ekt

You will be given this formula on the test, but will need to know what the variables represent.

N= Population number (final) No = Original population numbere= natural e ( a constant of 2.718… which will be on your scientific calculator)k = growth rate- You must use the decimal form for the formula (If 3.5% growth rate- use 0.035)t= time

To enter growth formula on calculator, enter No and then use 2nd function for ex. Be sure to have both r and t in parentheses for exponent.

Nigeria currently has a growth rate of 2.27%Its population in 2009 was 162 million.

A.If its growth rate stays the same, what will Nigeria’s population be in 2025? B.In 2050?

For this question, you are solving for N so use the formula : N =No ekt

A. No = 162 million (1.62 x 108)k = 0.0277 (decimal form of 2.77%)t = 16 years

N = 1.62 x 108 x e(0.0277 x 16)

= 2.52 x 108 (252 million people)

B.t= 41 yearsN = 1.62 x 108 x e(0.0277 x 41)

= 5.04 x 108 (504 million people)

The versions of the population growth rate formula rewritten to solve for either time or growth rate are shown below.

t = 1/k ln (N/No)k = 1/t ln (N/No)

You will be given these versions of the formula on the test as well.

Always be sure to identify what factor you are solving for to select the appropriate version of the formula.

The population of the Philippines was approximately 68 million in 1995. It was approximately 88 million in 2007. What was the average population growth rate during this time period?

For this question, you are solving for k, so use the formula : k = 1/t ln (N/No).

t = 12 yearsN = 8.8 x 107 (88 million)No= 6.8 x 107 (68 million)

k = 1/12 ln (8.8/6.8) = 0.0214 or 2.14%

The growth rate of Peru is 1.15 %. Its population is 29,400,000. How many years will it take for its population to reach 40,000,000?

For this question, you are solving for t, so use the formula : t = 1/k ln (N/No).

k = 0.0115 (decimal form of 1.15%)N = 4.0 x 107 (40 million)No = 2.94 x 107 (29,400,000)

t = (1/0.0115) ln (4 / 2.94) = 26.8 years

Rule of 70

Doubling time of a population = 70 / Growth rate (as a percentage)

You will need to memorize this formula for the test. And remember that you use the growth as a percentage in this formula (2.5 if 2.5% growth) as opposed to the decimal form in the growth rate formula.

Liberia is currently the country with greatest population rate in world, with a rate of 4.5 % (according to UN data) How many years will it take for its population to double (from 3.8 million to 7.6 million ) if it maintains this population growth rate?

The doubling time = 70/ 4.5 = 15.6 years