Idea 14of 22Builds onThe mean: level the stacks
Above and below the mean balance
Why does levelling always work out exactly?
Today you'll discover
- what sticks out above the mean
- what is missing below it
Think firstBooks read: 2, 3, 3, 4, 8. The mean is 4.
Eli's 8 is 4 above the mean of 4. How far below 4 are the others, altogether?
Decide first, then press Next. Compare the shaded tops with the dashed gaps.
Five stacks: 2, 3, 3, 4 and 8, with a dashed line at the mean, 4. The part of the 8 above the line is shaded and marked +4; dashed boxes between the short stacks and the line are marked −2, −1 and −1. A line below reads: above the mean 4, below it 2 + 1 + 1 = 4. The last step shows kilometres biked over five days.
See the whole ideathe big idea and the key word, in one place
The big idea
The amounts above the mean always equal the amounts below it: the mean is the balance point.
Why it balancesLevelling moves the extra into the gaps, and nothing is lost or added. So the extra and the gaps must be the same size.
Key word
- balance point
- the value where the amounts above it equal the amounts below it; the mean is the balance point
Ready to use it?
- Check a mean by comparing amounts above and below it.