Everything Maths Grade 10

7.The price of popcorn and a cooldrink at the movies is now R 60. If the average rate of inflation is 9,2%

p.a. what was the price of popcorn and cooldrink 5 years ago?

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Population growth EMA6T

Family trees increase exponentially as every person born has the ability to start another family. For this reason
we calculate population growth using the compound interest formula.

Worked example 11: Population growth

QUESTION

If the current population of Johannesburg is 3 888 180, and the average rate of population growth in South

Africa is 2,1% p.a., what can city planners expect the population of Johannesburg to be in 10 years?

SOLUTION

Step 1: Write down the known variables

P=3 888 180

i=0,021

n= 10

Step 2: Write down the formula

A=P(1 +i)n

Step 3: Substitute the values

A=3 888 180(1 +0,021)^10

=4 786 343

Step 4: Write the final answer

City planners can expect Johannesburg’s population to be 4 786 343 in ten years time.

346 9.4. Calculations using simple and compound interest