Random Variables

Mean and spread of a random number

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

• A random variable is a number decided by chance. Its distribution gives each value’s probability.
• Mean $\mu = \sum xP(x)$.
• Variance $\sigma^2 = \sum (x - \mu)^2 P(x)$. The standard deviation is $\sigma$.

Steps

1. A number decided by chance
2. The mean
3. The variance
4. The balance point
5. Linearity of expectation
6. Scaling up the stakes