Growth and decay

What this chapter teaches

Growth and decay by a fixed percent are repeated multiplication. A fall of 15% a year multiplies by 0.85 each year. The graph of decay falls quickly at first and then flattens, but stays above zero. The graph of growth bends upward.

Three questions to ask

There is no one right wording. Listen for the idea.

1. What do you multiply by each year if something falls by 15% a year?
2. Why does a rise of 10% a year for 2 years not make a rise of 20%?
3. Why does the decay curve never reach zero in the model?

After the chapter, the learner can

• Use the multiplier 0.85 for a 15% fall each year
• Model a goat herd that grows by 10% a year