Interpreting Tables, Spreadsheets, and Graphs

Step one: read the labels before the numbers

No matter what kind of chart you are facing, look at four things first. This 10-second scan stops almost every careless error:

• The title. It tells you what the whole chart is about (for example, "Monthly Sales").
• The axes. On a graph, the bottom line (the x-axis, going across) and the side line (the y-axis, going up) each have a label and units. Read what they measure.
• The scale. Check how much each gridline is worth. Going up by 1? By 10? By 1000? Getting this wrong is the most common mistake of all.
• The legend (key). If there is more than one colour or pattern, a small box explains what each one means. Match the colour to the label before you read a value.

A bar graph to read from

Here is a bar graph showing how many units a small shop sold each month. We will use it for the next two worked examples. Notice the title, the labelled axes, and the scale that goes up by 10.

The height of each bar lines up with the scale on the left. Read across from the top of a bar to the y-axis to find its value.

Worked example #1: reading a single value

Question: How many units were sold in April?

• Find the bar: look along the x-axis for "Apr."
• Read its height: trace from the top of the April bar straight across to the y-axis. It lands at 45.

April bar  →  top sits at 45 on the scale
Answer: 45 units

Worked example #2: comparing and combining values

Question: How many more units were sold in April than in January, and what were the total sales for January and February together?

• Read both bars: April = 45, January = 20.
• Subtract to compare: 45 − 20 = 25 more units in April.
• Add to combine: January (20) + February (35) = 55 units.

Difference:  45 − 20 = 25 units
Combined:    20 + 35 = 55 units

Reading tables and spreadsheets

A table is just a grid of rows (going across) and columns (going down). A spreadsheet is the same idea, with column letters (A, B, C…) along the top and row numbers down the side. To find a value, line up the right row with the right column, where they meet is your answer (a cell).

The main graph types, and what each one is for

• Bar graph: separate bars compare amounts across categories (months, products, regions). Taller bar = bigger amount.
• Line graph: points joined by a line show how something changes over time. A line going up means increasing; going down means decreasing. Great for spotting trends.
• Histogram: looks like a bar graph, but the bars touch and the x-axis shows ranges of numbers (like 0–9, 10–19). It shows how often values fall in each range.
• Circle (pie) graph: a circle cut into slices shows parts of a whole. A bigger slice is a bigger share. All slices add up to 100%.
• Scatterplot: a cloud of dots, each one a pair of values. If the dots drift upward together, the two things tend to rise together; if they drift downward, one rises as the other falls.

Worked example #4: spotting a trend and reading a slice

Part A (line graph). A line graph of a town's population shows the points 4,000 in 2021, then 4,300, 4,600, and 4,900 in 2024. Is the population rising or falling, and by about how much per year?

• Trend: each point is higher than the last, so the line rises, the population is increasing.
• Rate: it goes up about 300 each year (4,300 − 4,000 = 300, and the same gap repeats).

Part B (circle graph). A pie chart of a budget shows Rent 40%, Food 25%, Transport 15%, and Other 20%. If the monthly budget is $2,000, how much goes to Food?

Food = 25% of $2,000
     = 0.25 × 2,000
     = $500

Tips that prevent silly mistakes

• Check the scale every time. If gridlines jump by 10 (or 100, or 1000), a bar between two lines is not "between 1 and 2", read the actual numbers.
• Match the question word to the operation. "How many more" or "difference" means subtract; "total" or "altogether" means add; "of" with a percent means multiply.
• Use the legend before reading any coloured value. Reading the wrong line or bar is an easy trap when a graph has more than one series.
• For trends, look at the overall direction. Up, down, or flat? Do not get distracted by one small wobble.

Your turn: practice problems

Use the Monthly Units Sold bar graph above for questions 1–3, and the budget pie chart from example #4 for question 4. A calculator is fine. No peeking until you have tried.

1. How many units were sold in February?
2. Which month had the highest sales, and how many units was that?
3. What were the total units sold across all five months?
4. Using the budget pie chart (Rent 40%, total $2,000), how much goes to Rent?