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Proportional Reasoning-2

One circle for the whole set

Forty learners voted on their favourite game. Cut one circle into 40 equal parts called wedges. The circle can stand for all forty.

A full circle — one whole turn.
Step 1 of 4
  1. A full circle — one whole turn.
  2. Cut into 40 equal wedges, one per voter.
  3. One wedge, on its own: 9°.
  4. 40 × 9° = 360°.

A pie chart is a circle that stands for a whole set. Here the set is all 40 voters. A slice is one group's part of the circle. The whole circle is one full turn, 360° (360 degrees).

Each voter is one member of the set. A member's share is that member's part of 360°.

Rule: One member's share is 360° ÷ the number in the set.

The equal shares fill the whole circle. So we divide 360° by the number in the set.

Try other sets. 24 learners give 360 ÷ 24 = 15° each. 200 learners give 360 ÷ 200 = 1.8° each. The circle stays the same size. Only each member's share changes.

Drag the slider. Watch one wedge change size.

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This track

  1. 0 Start here
  2. 1 One circle for the whole set
  3. 2 A slice is a share of the turn
  4. 3 Draw a chart, then check it closes
  5. 4 What a chart says, and what it holds back
  6. 5 Two charts that look the same
  7. 6 When one grows and the other shrinks
  8. 7 Which kind is it, or neither
  9. 8 Workers and days, speed and time
  10. 9 A ratio with three parts
  11. 10 Share a whole in many parts
  12. 11 Checkpoint: ratios with many terms
  13. 12 The big picture
  14. 13 Track quiz

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