A table organizes information, but the question determines which cells and relationships matter. Before calculating, read the headings, units and any notes about what has been counted.
Compare the right quantities
Two groups complete a practice activity:
| Group | Participants | Completed |
|---|---|---|
| A | 40 | 30 |
| B | 80 | 48 |
Group B has more completions: 48 compared with 30. Group A has the higher completion rate: 30/40 = 75%, compared with 48/80 = 60%. More and higher rate are different questions.
Combine the groups correctly
Together there are 120 participants and 78 completions. The overall completion rate is 78/120 = 65%.
Averaging 75% and 60% gives 67.5%, which incorrectly weights the unequal groups equally. When combining rates, return to the underlying counts whenever possible.
Check whether categories overlap
If a survey allows several answers, adding category totals may count the same person more than once. A table showing people who selected A and people who selected B does not necessarily show two disjoint groups.
Look for wording such as choose one, select all that apply or unique participants. Do not infer a grand total from overlapping categories without enough information.
Read missing values carefully
A blank cell can mean unavailable, not applicable or omitted. It does not automatically mean zero. Use any legend supplied. If none is given, avoid inventing a value to complete the arithmetic.
Work from the question backward
Underline mentally what is requested: difference, proportion, total or trend. Identify the needed numerator and denominator, calculate and then state the answer with the correct unit. This approach reduces unnecessary work and protects against a common mistake: doing a correct calculation with the wrong pair of cells.