SME
Grade 9 Math
Exponential functions: growth and decay
The main lesson, then each kind of problem it solves.
Exponential functions: growth and decay
Main lesson
Growth by a percent
Use this for “$800 earns 3% a year, compounded yearly. How much after 4 years?”
Decay by a percent
Use this for “A $18,000 car loses 15% of its value each year. In which year is it first worth under $9,000?” Read down the table.
Solve by writing the same base
Use this for “Solve 4⁶ = 8ˣ.”
Doubling time
Use this for “400 cells double every 3 hours. How many are there after 12 hours?”
Linear or exponential?
Use this for “Which model fits: does it add the same amount or multiply by the same factor each step?”