① Reading bar chartsNo calculator
Read the height of each bar against the scale. Check how much each gridline is worth.
② Reading pie chartsNo calculator
The whole circle is 360°. A sector is a fraction of the whole, so find the fraction of the total. Some pie charts show the angles (a small square means 90°) and some show how many chose each.
③ Calculating pie chart anglesCalculator useful
Find the angle for one item, then multiply by each frequency. The angles must add up to 360°.
④ Fractions and percentages from chartsCalculator useful
Write each amount as a fraction of the total, then simplify or convert to a percentage.
⑤ Working backwards from the anglesCalculator useful
If you know how many are in one sector, its angle tells you the fraction of the whole. Use it to find the total, then the number in any other sector.
Key steps
Bar charts: look at what each gridline is worth before reading a value.
Pie charts: the angles add up to \(360^\circ\). A sector is \(\dfrac{\text{angle}}{360}\) of the total.
Drawing pie charts: angle = \(\dfrac{\text{frequency}}{\text{total}}\times360\).
Fractions: write the part over the total, then simplify.
Working backwards: total = number in a sector × \(\dfrac{360}{\text{angle}}\). When the group changes size, work out the new total before finding the new angle.