Lesson 9 of 11
The big picture
Show on a big screenThe pencil balanced on the ruler showed the mean all along.
| Idea | Remember | Example |
|---|---|---|
| Balance point | The mean is where numbers balance | 20,22,24,26,28 balances on 24 |
| Above and below | The two sides always match | 4,6,3,12,5: both sides total 6 |
| Moving one | Move ÷ count = mean's move | +10 on one of five, mean +2 |
| Adding one | Compare with the current mean | ₹500 below ₹620 pulls the mean down |
| Two groups | Rebuild the totals, then share | 4×20 + 6×30, over 10, is 26 |
| Joining dots | Join when the bottom scale has a real order | Weeks join; book kinds do not |
| Reading the line | Change ÷ steps = steepness | 17 cm over 4 h is 4.25 cm an hour |
| Drawing honestly | The scale changes the impression | 0–56 looks small; 44–56 looks big |
Part II, Chapter 5 is Tales by Dots and Lines. Read the chapter and meet these ideas again.
Given a mean, ask how many readings it was made from. Given a line, check the bottom scale. Check where the side scale starts.