O Level MathematicsC9.4 Displaying data (frequency tables, bar charts, pie charts, stem-and-leaf diagrams).

πŸ“Š Data Made Visible! Mastering Frequency Tables, Charts & Diagrams

Edudent Academy
6 Feb 26

Collecting numbers is only half the jobβ€”**displaying data clearly** lets us spot patterns, make comparisons, and earn easy marks in the O Level exam. In this post you’ll learn the four core methods examiners expect: frequency tables, bar charts, pie charts and stem-and-leaf diagrams.

Essential Display Methods

1. **Frequency table** – Organises raw scores with tally marks and totals so data can be quickly read. 2. **Bar chart** – Uses equal-width bars; the height of each bar equals the frequency. Bars must be evenly spaced. 3. **Pie chart** – Shows parts of a whole. Remember the angle rule: SectorΒ angle=frequencytotalΓ—360∘\text{Sector angle}=\dfrac{\text{frequency}}{\text{total}}\times360^\circ. 4. **Stem-and-leaf diagram** – Splits each value into a *stem* (leading digit) and *leaf* (final digit). It keeps the original data visible and is great for identifying the median & mode.

Worked Example: Pet Survey

  • Problem: 30 students were asked which pet they kept at home. The results were: Dog 12, Cat 9, Fish 6, Hamster 3. Display the data in (i) a frequency table, (ii) a bar chart and (iii) a pie chart.
  • Step 1: Construct a frequency table listing each pet and its count.
    PetFrequencyDog12Cat9Fish6Hamster3\begin{array}{|c|c|}\hline\text{Pet}&\text{Frequency}\\\hline\text{Dog}&12\\\text{Cat}&9\\\text{Fish}&6\\\text{Hamster}&3\\\hline\end{array}
  • Step 2: Draw a bar chart with four equal-width bars. Label the horizontal axis with pet types, the vertical axis with frequency, and scale up to 12.
  • Step 3: Find each pie-chart angle using
    ΞΈ=f30Γ—360∘\theta=\frac{f}{30}\times360^\circ
    so Dog =1230Γ—360∘=144∘=\frac{12}{30}\times360^\circ=144^\circ, Cat =108∘=108^\circ, Fish =72∘=72^\circ, Hamster =36∘=36^\circ. Sketch a circle, mark the angles in order, shade and label each sector.