Data Interpretation — CDS Elementary Mathematics

Formulas (2)

• Percentages and percentage change · Percentage change
  $$\dfrac{\text{new} - \text{old}}{\text{old}} \times 100$$
• Totals, averages and closest-to-average · Average
  $$\bar x = \dfrac{\text{total}}{n}$$

Watch out for (3)

• Divide by the OLD figure
  → Percentages and percentage change
• 'More than' versus 'more than or equal to'
  → Percentages and percentage change
• Which average?
  → Totals, averages and closest-to-average

Formulas (2)

• Angle, share and count · Sector angle
  $$\theta = \dfrac{\text{value}}{\text{total}} \times 360^\circ$$
• Comparing charts with different totals · Share to count
  $$\text{count} = \dfrac{p}{100} \times \text{total}$$

Watch out for (3)

• The total changes too
  → Angle, share and count
• Radius is not the total
  → Angle, share and count
• Same share is not the same size
  → Comparing charts with different totals

Formulas (1)

• Year-on-year change and percentage bars · Segment of a percentage bar
  $$\text{length} = \dfrac{x}{T} \times H$$

Watch out for (1)

• A doubling is 100%, not 200%
  → Year-on-year change and percentage bars

Formulas (1)

• Build the table first · Missing cell
  $$\text{cell} = \text{row total} - \text{known cells}$$

Watch out for (1)

• A percentage of which total?
  → Build the table first