7.1 Tables, Charts & Data Reading

7.1 Tables, Charts & Data Reading

Quick Answer: On data-reading items, find the exact cell, bar, sector, or point the question names, note the units, then compute only the required sum, difference, average, or percentage. Never invent missing values. A neighbouring row or a total mistaken for a part is the most common trap.

The Service Commissions Department (SCD) lists Mathematics among the three multiple-choice subjects in its published entrance-examination notices. Data reading—tables, simple charts, and everyday numerical displays—is classic civil-service exam skill. You are not expected to design surveys or run statistical software. You are expected to locate the right figure, respect units, and finish a short calculation without mixing up rows, columns, or categories.

This section uses civilian Trinidad and Tobago examples: school or event attendance, market prices, and rainfall summaries presented as general practice data. It does not invent official exam formats, item counts, or fireground technical tables.

Why data items trip candidates

Many wrong answers come from haste, not hard arithmetic:

1. Reading the wrong row (next community or next day).
2. Ignoring units (mm vs cm; $ vs $000).
3. Treating a total row as if it were one category.
4. Comparing bars by height roughly instead of reading the scale.
5. Using a pie slice “looks biggest” without checking labels or percentages.

Build a fixed routine: title → labels → units → exact value → calculate → check.

Tables — rows, columns, and cells

A table organises related numbers so you can look up one fact quickly.

Worked example — community centre attendance

A community centre in Chaguanas records Saturday class attendance for four weeks:

Question pattern A — single cell: How many youth attended in Week 2?
Locate row Week 2, column Youth → 35.

Question pattern B — difference: How many more adults attended in Week 3 than in Week 2?
45 − 38 = 7.

Question pattern C — total of a column (if not given): Adults over four weeks: 42 + 38 + 45 + 40.
42 + 38 = 80; 80 + 45 = 125; 125 + 40 = 165 adults.

Question pattern D — check a total: Week 1 total should be 42 + 28 = 70. Matches the table. If a question gives a broken total, trust the parts and recompute.

Trap — wrong week, right column

If the stem says “Week 4 youth” and you glance at Week 3 youth (30), you miss the answer 32. Always put a mental finger on the row label first, then move across to the column.

Trap — using the total instead of a part

“What share of Week 2 attendance was youth?” needs youth ÷ total = 35 ÷ 73, not 35 ÷ (38 + 35) done carelessly or 73 alone.
35 ÷ 73 ≈ 0.479 ≈ 48% if the question asks for a nearest whole percent.

Bar charts — comparing categories

A bar chart uses bar length (or height) to compare values for categories. Horizontal and vertical bars carry the same idea.

Reading steps:

1. Read the chart title.
2. Read the category labels (x-axis or bar labels).
3. Read the scale on the value axis (what each mark means).
4. Estimate or read each bar’s value from the scale.
5. Compute only what the question asks (largest, difference, sum of two, etc.).

Worked example — market stall prices

A chart (described in words for study) shows the price of 1 kg of tomatoes at four market days:

If drawn as bars, Saturday’s bar is tallest; Monday’s is shortest.

• Highest price day: Saturday ($18/kg).
• Difference Saturday − Monday: 18 − 12 = $6.
• Mean of the four prices: (12 + 15 + 14 + 18) ÷ 4. Total = 59; mean = 14.75 TTD/kg.

If the scale is marked every 2 dollars, a bar ending halfway between 14 and 16 is 15, not 14 or 16. Half-marks matter.

Comparative language in stems

Pie charts — parts of a whole

A pie chart shows how a whole is split into parts (sectors). The whole is usually 100% or a known total count.

Rules of thumb:

• All sector percentages should sum to 100% (allowing for rounding).
• A sector of 25% is a quarter of the circle; 50% is half.
• To find a count from a percent: part = percent × total ÷ 100.
• To find a percent from a count: percent = part ÷ total × 100.

Worked example — household budget shares

A household’s monthly “discretionary” budget of $2,000 is shown as:

• Transport amount: 30% of 2,000 = 0.30 × 2,000 = $600.
• Food extras: 0.40 × 2,000 = $800.
• Recreation + savings: 15% + 15% = 30% → $600 combined.
• Check: 600 + 800 + 300 + 300 = 2,000. Good.

If two sectors look similar but labels say 15% and 18%, trust the labels, not your eye.

Line ideas — ordered change over time

A line graph (or a simple series of points joined in order) shows how a quantity changes across an ordered set—often days, months, or years.

You mainly need:

• Trend: rising, falling, or roughly flat.
• Highest / lowest point on the series.
• Change between two points: later value − earlier value (can be negative).
• Simple average of several plotted values if asked.

Worked example — monthly rainfall summary (practice data)

A rainfall summary for a coastal station lists monthly totals (mm) for four months:

• From Jan to Feb, rainfall fell by 60 − 45 = 15 mm.
• From Feb to Mar, it rose by 80 − 45 = 35 mm.
• Wettest of the four: March (80 mm).
• Four-month total: 60 + 45 + 80 + 70 = 255 mm.
• Mean monthly: 255 ÷ 4 = 63.75 mm.

If a line is drawn through these points, March is the peak; February is the trough. Do not invent values between months unless the question gives them.

Combining skills — table plus percentage

Attendance at a Port of Spain workshop:

• Morning attendance rate: 44 ÷ 50 = 0.88 = 88%.
• Afternoon rate: 36 ÷ 40 = 0.90 = 90%.
• Overall present: 44 + 36 = 80; overall registered: 50 + 40 = 90; overall rate: 80 ÷ 90 ≈ 88.9%.

Notice: afternoon has a higher rate even though fewer people attended. Rate questions need division, not only raw counts.

Unit and scale discipline

Always write the unit in your working:

• Rainfall in mm vs cm (10 mm = 1 cm).
• Money in TTD.
• People as whole counts unless the question uses averages that can be decimals.
• Scales marked “in hundreds” mean a bar at 3 may mean 300, not 3.

If two charts use different scales, you cannot compare bar heights by eye across charts—convert to actual numbers first.

Exam-day checklist for data items

1. Underline what the question wants (one cell, a difference, a %, a max).
2. Identify every category or time period named.
3. Extract only those numbers from the display.
4. Perform the arithmetic on scrap paper.
5. Re-check: did you use the total row by mistake? Wrong week? Wrong unit?
6. Match your result to the options; if none match, re-locate the cells before redoing the whole sum.

What this section does not claim

• No published SCD Fire entrance blueprint of “how many chart questions.”
• No requirement for advanced regression, histograms with class intervals, or professional weather analysis.
• No firefighting hydraulics, pump charts, or technical fireground tables.

Master careful extraction + short arithmetic. That combination scores points on Mathematics data items under timed multiple-choice conditions.

Practice habit

When you review any newspaper table, school notice, or market price list:

• Ask one lookup question (“What was Tuesday’s figure?”).
• Ask one comparison (“Which day was highest?”).
• Ask one calculation (“What was the two-day total / mean / difference?”).

That three-question habit builds the exact skill this section trains.