Two Numbers Run the Whole Model

You'll learnto pull a starting value and a growth factor out of a story, a table, or a doubling time.

Every exponential model comes down to two decisions: where does it start, and what does one step multiply by? Contexts hide those two numbers behind percent language, pairs of data points and doubling times, and each hiding place has its own way of going wrong. Watch both numbers get pulled out of four different stories, and watch why a 12% loss is a factor of 0.88 rather than 0.12. Twelve short steps; press Next for each one.

12 STEPS · 6 QUICK CHECKS · f(x) = a·b^x · b = 1 + r · v3

where it starts · what one step multiplies by

Before you start

What you're looking at

Four real situations — a colony, a pond, a car and a cell culture — each drawn as a curve or a bar chart.

The question

Where does the model start, and what does one step multiply by?

Step 1 / 12