Question

Stacey buys a $1000 RRSP today. After one year she adds $2500. By the end of the second year, the money has grown to $3851 as it has earned interest over time. What rate of interest does the money earn?

1000x^2 + 2500x - 3851

Use the quadratic formula above and your calculator to solve for x and i.

There are two solutions to the quadratic equation. Which one would you choose? Why?

Answer 1

Choose the solution that makes sense. Most of the time only the positive solution makes sense.

Answer 2

Simple example:

I drop a ball from 16 feet up. Its height can be modeled as h = -16t^2 + 16, where h = height in feet and t = time in seconds. When will the ball hit the ground?

16t^2 - 16 = 0
t = -1, 1

It took -1 second? No way.
It took 1 second? Yes!