The Bell Curve

Normal distributions

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• Sums of many random effects tend toward a bell curve (the central limit theorem).
• 68–95–99.7: the share of values within 1, 2 and 3 standard deviations of the mean.
• Use symmetry for one-sided questions: split the outside share between the two tails.

Steps

1. Add up dice
2. The 68–95–99.7 rule
3. Heights
4. Very high scores
5. One standard deviation up
6. A lopsided range