Cambridge Syllabus Notes

16 Graphs and charts – Adding a Second Data Series

Objective

Be able to add a second data series to a graph or chart in a spreadsheet or presentation tool.

Why Add a Second Series? 📈

Think of a graph as a race track. The first data series is one runner. Adding a second series is like inviting a friend to race on the same track. It lets you compare two sets of data side‑by‑side, spotting trends, differences, or relationships. In exams you’ll often need to show how two variables change together (e.g., temperature vs. ice‑cream sales).

Step‑by‑Step Guide

Choose your chart type. For most comparisons, use a line chart or column chart.
Enter the first data series. Label the X‑axis (e.g., months) and Y‑axis (e.g., sales). Input the values in two columns: Month and Sales1.
Insert the chart. Highlight the data and click Insert → Chart. A default chart appears.
Add the second series.
- In Excel: Right‑click the chart → Select Data → Add → choose the new Y‑column (e.g., Sales2) and give it a name.
- In Google Sheets: Click the chart → Chart editor → Series → Add series → select the new column.
Format the series. Give each series a distinct colour or line style so they’re easy to tell apart.
Check the legend. Make sure the legend shows both series names.
Review. Verify that the chart now displays two lines/columns, each representing one data set.

Example: Comparing Two Products

Month	Product A Sales	Product B Sales
Jan	120	80
Feb	150	95
Mar	170	110

After inserting a line chart and adding both series, you’ll see two lines: one for Product A and one for Product B. Notice how the slopes differ, indicating different growth rates.

Exam Tips & Tricks 🧩

Label everything. In the exam, always label the X‑axis, Y‑axis, and each data series. This shows you understand the chart’s components.
Use contrasting colours. If you’re drawing the chart by hand, pick colours that are easy to distinguish (e.g., blue vs. red). For digital charts, use the default colour palette or the “colour‑blind friendly” option.
Check the legend. The legend should match the series names you used in the data table.
Interpret the trend. After adding the second series, describe what the comparison tells you. For example, “Product A’s sales grew faster than Product B’s over the first quarter.”
Time your work. Practice adding a second series quickly; you’ll save time during the exam.

Quick Math Check

If you want to calculate the percentage increase between two months for a series, use: $$\text{Percent Increase} = \frac{\text{New Value} - \text{Old Value}}{\text{Old Value}} \times 100\%$$ For example, from Jan to Feb for Product A: $$\frac{150 - 120}{120} \times 100\% = 25\%$$

Remember!

Adding a second data series is like adding a new layer to a story. It gives depth and lets you compare, contrast, and discover relationships. Keep practising, and you’ll master this skill in no time! 🚀

Be able to add a second data series