Lesson 12 of 14
The big picture
Show on a big screenPie charts, many-term ratios, then inverse proportion.
| Idea | Remember | Example |
|---|---|---|
| The whole turn | 360° shared out over the whole set | 40 voters → 9° each |
| A slice | count × one member's share | 15 × 9° = 135° |
| Drawing one | count, share, angle, draw, check | 150+90+72+48 = 360 |
| Reading one | shares only; a count and its slice give the total | 90° = 18 → 72 in all |
| Two charts | same shares, different totals | 15/40 = 75/200 |
| One up, one down | the product stays fixed | 6×12 = 8×9 = 72 |
| Which kind | ÷ for direct, × for inverse, or neither | an auto fare = neither |
| At work | multiply, divide, multiply back | 72÷9=8, then 9×8=72 |
| Many terms | Multiply every term by the same number. Find that number from the amount you know. | 3 : 5 : 4 → 6 : 10 : 8 |
| Sharing a whole | Add the terms. Divide the whole by that sum. Multiply each term by the answer. | ₹4,500 in 4 : 3 : 2 → ₹500 a part |
Part II has this as Chapter 3, Proportional Reasoning-2. Open it and use these ideas.
One question links the two ideas. What stays the same? A pie chart's angles total 360°. An inverse pair's product stays fixed.