Data Interpretation Notes

Data Interpretation

Reading the four sets an exam uses — table, bar chart, line graph and pie chart — plus mixed and caselet sets; the five questions they ask (total, average, ratio, percentage share and percentage change); reading the heading and the unit before the numbers; approximation and elimination under time pressure; percentage change versus percentage point; converting a pie chart between percent, degrees and absolute values — with a full worked set.

Last reviewed 22 Sept 2026 · 5 min read

What a DI set really tests

Not arithmetic — reading. Nearly every mark lost in this section comes from one of four things: the unit in the heading (lakh, crore, thousand), the row or column read one line off, "percentage increase" mistaken for "percentage point", or an average taken over the wrong number of years.

Read in this order: title → unit → row and column headings → the question. Only then look at the numbers.

The four presentations

Type	What it is good at	Watch out for
Table	exact values, several variables	which way the years run
Bar chart	comparing quantities	the scale, and bars that do not start at zero
Line graph	trend over time	a broken axis exaggerating a rise
Pie chart	shares of one whole	two pies with different totals

A caselet presents the same data as a paragraph of prose; convert it into a small table before answering anything.

The five questions

FormulaThe recurring calculations

Total of a row or column — plain addition
Average $= \frac{total}{number of entries}$ (count the entries, do not assume five)
Ratio — reduce before dividing
Percentage share $= \frac{part}{whole} \times 100$
Percentage change $= \frac{new - old}{old} \times 100$ — always over the old value

For pie charts: $1% = 3.6°$ , so a sector of $54°$ is $15%$ . Two pie charts can only be compared in absolute terms if both totals are given.

Working quickly

Keep the unit out of the arithmetic: if everything is "₹ lakh", work in plain numbers and put the unit back at the end.
Use fraction equivalents rather than long division: $\frac{1}{8} = 12.5%$ , $\frac{1}{7} \approx 14.3%$ , $\frac{1}{6} \approx 16.7%$ , $\frac{1}{3} \approx 33.3%$ .
When options are far apart, approximate: $\frac{85}{180}$ is a little under half, so 47% is right and 43% is not.
Do not recompute a total you already worked out for the previous question — DI sets are built so each answer feeds the next.

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