Salma puts $1 000 into the bank. The bank pays 10% interest per year. How long is it before Salma has $1 500 in her account?

And in order to plot the graph, we needed points (from some simple calculations) After 1 full year, she has $1000 x 1.1 or $1100 After 2 full years, she has $1000 x (1.1) 2 or $1210 After 3 full years, she has $1000 x (1.1) 3 or $1331 and so on …

Time (in full years)Amount of money ($)

The red curve shows the growth of the money in the account We now need to find when the y-coordinate reaches 1500 (hence the blue line)

Geogebra will give the coordinates of the point of intersection (point A on the diagram) The answer is – Salma will have $1500 after years.

The growth of Salma’s money is described by the equation: A = 1000 x (1.1) t And we simply want to solve the equation 1500 = 1000 x (1.1) t This simplifies to 1.5 = (1.1) t Taking logs of both sides … log = log t ⇒ t = log log ⇒ t = years ⇒ log = tlog (using one of our rules of logs)

To some degree the population is growing like Salma’s money Some questions … What’s the starting population? What is the percentage increase per year of the population?

Or this ….