CDS Mathematics · Data Interpretation

Caselets: Data Given in Words

A caselet gives its data as a paragraph; turn it into a table first, filling every cell, and each question becomes a lookup.

All Data Interpretation notes CDS Mathematics strategy

Why this matters

Five PYQs, all from one 2017 paragraph about students by subject and gender. The paragraph gives some cells as counts, some as fractions and some only as 'the rest', so the only safe method is to build the full table once and answer every item from it.

Concept 1 of 1: Build the table first

Every fact in the paragraph fills one cell. Row and column totals then fill the cells the paragraph left out. Once the table is full, the questions only ask you to read it.

Definition

Draw rows for the categories and columns for the split (boys and girls), with totals.
Convert fractions and percentages to counts using the right total: ' $60\%$ of Physics students' is $60\%$ of the Physics row.
Fill 'remaining' cells last, from the totals.
Check that the grand total adds up before answering.

Missing cell

\text{cell} = \text{row total} - \text{known cells}

Worked example

A college has

600

students:

25\%

in Arts,

240

in Science and the rest in Commerce.

40\%

of Science students are girls. How many boys study Science, and how many students study Commerce?

Practice this conceptself-check · 4 quick reps

The same idea in a real exam question:

CDS · 2017 · CDS (II) 2017 — Elementary Mathematics · Q86Moderate

Example 1 · Data Interpretation · Caselet Data Interpretation

for the items that follow : In a University there are 1200 students studying four different subjects, Mathematics, Statistics, Physics and Chemistry. 20% of the total number of students are studying Mathematics, one-fourth of the total number of students are studying Physics, 320 students are studying Statistics and remaining students are studying Chemistry. Three-fifth of the total number of students studying Chemistry are girls. 150 boys are studying Mathematics. 60% of students studying Physics are boys. 250 girls are studying Statistics.

What is the total number of boys studying Statistics and Physics ?

A percentage of which total?

60\%

of students studying Physics are boys' is

60\%

of the Physics row, not of the whole university. Using the grand total is the usual slip.

Drill 4 more on build the table first

Summary — formulas & gotchas at a glance

A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.

Formulas (1)

Build the table first
Missing cell
$\text{cell} = \text{row total} - \text{known cells}$

Watch out for (1)

A percentage of which total?
→ Build the table first

Test yourself on a real paper

Sit a past CDS paper, timed and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.

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