Venn Diagrams: Choosing the Diagram and Reading Regions
Venn Diagrams: Choosing the Diagram and Reading Regions
A Venn diagram shows how classes relate: one inside another, overlapping, or completely separate. NTPC asks you to pick the diagram that fits three classes, and to read a given diagram with numbered regions or numbers written inside. Decide each pair first (inside, overlap or separate), then combine.
1. Pair Relations
| Relation between two classes | Drawing | Example |
|---|---|---|
| One is a part of the other | Small circle inside a big one | Patna inside Bihar |
| Some are, some are not | Two overlapping circles | Teachers and singers |
| Nothing in common | Two separate circles | Dogs and cats |
2. Common Three-Class Diagrams
| Diagram (described) | Fits | Example |
|---|---|---|
| Three circles nested one inside another | A inside B inside C | Patna, Bihar, India |
| Two separate circles inside a big circle | Two kinds of one class | Dogs, Cats, Animals |
| Three mutually overlapping circles | Every pair overlaps | Teachers, Singers, Men |
| Small circle inside a big one, third circle overlapping both | A inside B, C overlaps both | Mothers, Females, Doctors |
| Small circle inside a big one, third circle separate | A inside B, C apart | Pacific Ocean, Oceans, Rivers |
| Three separate circles | No overlaps | Pens, Shoes, Rivers |
Test every pair before choosing: three pairs, three relations
Seven regions of three overlapping circles: three "only", three "exactly two", one "all three"
✗ Doctors and mothers both overlap females, so draw three overlapping circles | ✓ Every mother is female: mothers must lie inside females
✗ Only the region inside all three circles counts for "teachers who are men" | ✓ Teachers who are men but not singers is a separate region; read the exact wording
हिंदी नोट: वेन आरेख में पहले हर जोड़ी का संबंध तय कीजिए: अंदर, आंशिक रूप से साझा या पूरी तरह अलग। तीन वृत्तों के सात भाग होते हैं: तीन "केवल", तीन "ठीक दो" और एक "तीनों"।
Exam Pointer: Verified NTPC patterns: choosing the Venn diagram for three classes (February and March 2021 CBT-1) and reading numbered regions of a three-circle figure (January and February 2021 CBT-1). Questions with separate groups had no separate verified shift and are tagged syllabus-based.
Pariksha Pattern: Every Way NTPC Asks This Topic
Pattern 1: Choosing the diagram: nested and overlapping classes
[PYQ: NTPC CBT-1 9-Feb-2021 Shift-1 | NTPC CBT-1 11-Mar-2021 Shift-1]
EXAM LEVEL
Q. Which diagram best represents India, Bihar and Patna?
Patna is in Bihar and Bihar is in India: three circles nested one inside another.
Answer: Three nested circles
EXAMATLAS LEVEL
Q. Which diagram best represents Females, Mothers and Doctors?
Every mother is female, so Mothers lies inside Females. Some doctors are mothers, some are females who are not mothers, and some are male, so Doctors overlaps both circles and also extends outside Females.
Answer: Small circle (Mothers) inside a big one (Females), with a third circle (Doctors) overlapping both
Pattern 2: Choosing the diagram: separate groups
[Pattern: syllabus-based, PYQ-style]
EXAM LEVEL
Q. Which diagram best represents Dogs, Cats and Animals?
Dogs and cats have nothing in common, and both are animals: two separate circles inside one big circle.
Answer: Two separate circles inside a big circle
EXAMATLAS LEVEL
Q. Which diagram best represents Rivers, Oceans and the Pacific Ocean? Which best represents Teachers, Singers and Men?
The Pacific is one of the oceans, so its circle lies inside Oceans; rivers are separate from both. Teachers, singers and men overlap in every pair (a male singing teacher exists, and so do people in each part alone).
Answer: Small circle inside a big one with a third circle separate; three mutually overlapping circles
Pattern 3: Reading numbered regions
[PYQ: NTPC CBT-1 11-Jan-2021 Shift-2 | NTPC CBT-1 9-Feb-2021 Shift-2]
Figure for both questions: three overlapping circles T (teachers), S (singers) and M (men). Regions: 1 T only, 2 S only, 3 M only, 4 T and S only, 5 S and M only, 6 T and M only, 7 all three. The numbers of people in regions 1 to 7 are 12, 9, 15, 5, 7, 4 and 3.
EXAM LEVEL
Q. Which region shows teachers who are men but not singers?
Inside T and M, outside S: region 6.
Answer: Region 6
EXAMATLAS LEVEL
Q. How many singers are not men, and how many people belong to exactly two of the three groups?
Singers not men are regions 2 and 4: 9 + 5 = 14. Exactly two groups are regions 4, 5 and 6: 5 + 7 + 4 = 16.
Answer: 14; 16
Pattern 4: Describing a region in words
[Pattern: syllabus-based, PYQ-style]
Figure for both questions: circle U (urban people), triangle E (educated people) and square H (honest people) overlap. Regions: a U only, b E only, c H only, d U and E only, e E and H only, f U and H only, g all three.
EXAM LEVEL
Q. Which region represents educated, honest people who are not urban?
Inside E and H, outside U: region e.
Answer: e
EXAMATLAS LEVEL
Q. Which regions together represent urban people who are not honest, and which represent honest people who are educated?
Urban but not honest: inside U, outside H, regions a and d. Honest and educated: inside H and E, regions e and g.
Answer: a and d; e and g
60-Second Revision
- Decide each pair: inside, overlap or separate.
- Combine the three pair relations into one diagram.
- Three overlapping circles have seven regions; name them before counting.
- Read every "not" in the description carefully.