CLAT (Common Law Admission Test) · General Intelligence & Reasoning

Reasoning Data Sufficiency

Decide whether statement (I), (II), either, both, or neither suffice to answer a reasoning question — ranking and direction stems, not quantitative DS.

Five concepts. A banking-mains data-sufficiency item never asks you to name who stands where or which way Rahul faces. It asks whether statement (I), statement (II), either statement, both together, or neither is enough to know — a uniqueness test, not a full solve. The inner puzzles here are the office morning line (Priya, Rohan, Meena, and sometimes Anil, facing north) and Rahul's 90-degree turns from a named facing; those are already taught as ranking and direction. What is new is the five-option verdict.

CLAT (Common Law Admission Test)
Medium level
5 concepts
16 practice questions

1Five codes: I alone, II alone, either, both, neither

Banking mains data sufficiency does not ask you to name who is tallest or which way Rahul faces. It asks whether the printed facts are enough to know. A statement is sufficient when every arrangement (or every walk) that fits those facts gives the same answer to the question — one name, one rank, one facing. If two legal completions still disagree, the statement has failed, even if it feels helpful.

Each item gives a question plus two labelled statements, (I) and (II). You map the uniqueness test onto five codes. In this topic those codes are fixed: A means (I) alone pins the answer and (II) does not; B is the mirror ((II) alone, not (I)); C means each statement already pins the answer by itself; D means neither statement pins it alone but the two together do; E means even the two together still leave more than one possibility. Some bank papers swap D and E — they put 'neither' on D and 'both needed' on E — so the first move on a real paper is to read that paper's directions, not to recite this topic from memory.

The trap is treating the codes as a memory list and bubbling D because you happened to use both statements. Using a statement is not the test. Uniqueness is the test. The Codes used in this topic table is the map; alone-first, either, both-needed and neither are the four ways a pair of statements can land on that map.

Figure. This topic's codes: A is I alone, B is II alone, C is either, D is both needed, E is neither even together. A, B and C stay put; some bank papers reverse D and E.

How the codes work

Name the asked quantityRead the question first: a unique name, rank, facing or distance. That is the only thing that has to be pinned. Extra facts about people the question did not ask for are irrelevant.
Test uniqueness, not effortA statement is sufficient only when every legal completion gives the same answer. Two remaining names means failure, even if the field shrank.
Read this paper's A–EA, B and C are stable across papers (I alone / II alone / either). D and E swap on some bank papers. This topic uses D = both needed and E = neither; a live paper may reverse them.

A, B and C are stable. D and E are the pair some papers reverse — always re-read the directions on a live paper.

Codes used in this topic
Code	Means	Pick when
A	I alone (not II)	I pins one answer; II leaves two or more
B	II alone (not I)	II pins one answer; I leaves two or more
C	Either I or II	Each statement by itself pins one answer
D	Both needed	Each leaves two or more; together they pin one
E	Neither even together	Together they still leave two or more

I alone names the rank

In the four-person office row facing north, what is Rohan's position from the left? (I) Rohan is second from the left. (II) Meena is third from the left.

Asked: Rohan's left-rank in a 4-person rowneed a unique number 1–4
(I) Rohan is second from the leftposition = 2 in every completion — I sufficient
(II) Meena is third from the leftRohan in {1, 2, 4} — three answers, II fails
Code (this topic)A — I alone, not II

Pro tip. You never needed to place Priya or Anil. The question asked for Rohan's left-rank, and (I) already named it.

Priya, Rohan and Meena stand in a line facing north. Who is at the right end? (I) Priya is at the left end. (II) Meena is in the middle and Rohan is not at the left end. Using this topic's codes, the answer is

I alone sufficient (II not)
II alone sufficient (I not)
Either I or II alone sufficient
Both together necessary
Even both together not sufficient

(I) Priya at left leaves two line-ups: Priya–Rohan–Meena (right = Meena) and Priya–Meena–Rohan (right = Rohan). Two answers, so (I) fails. (II) Meena in the middle and Rohan not at the left forces Priya–Meena–Rohan; the right end is Rohan uniquely. Code B.

2Test each statement alone before combining

Once the five codes are in hand, the working order is rigid: test statement (I) by itself, then test statement (II) by itself, and only then — if both failed — put them together. Jumping to 'both needed' is the mark-loss, because a pair that works together often had one statement that already worked alone.

Watch the office height question. Who is tallest among Priya, Rohan and Meena? (I) Priya is taller than both Rohan and Meena. That already names Priya as the unique tallest — two of the six height orders survive, Priya > Rohan > Meena and Priya > Meena > Rohan, and both have the same tallest. (II) Rohan is taller than Meena. Three orders survive, and the tallest is Priya in one of them and Rohan in the other two, so (II) fails. Together they still say Priya, but you did not need (II). The code is A, not D.

The examiner writes the extra comparison on purpose. A solver who lines everyone up into Priya > Rohan > Meena has solved a ranking question nobody asked. Data sufficiency asked whether the facts were enough, and (I) already was.

Figure. Statement cards for the height item. (I) already pins Priya as tallest (sage). (II) still leaves Priya or Rohan (terracotta), so it is extra. Verdict is I alone — not both.

Order of attack

Cover (II)Hide statement (II). List every completion consistent with (I) and the question. One answer: (I) is sufficient. Two or more: (I) has failed.
Cover (I)Hide statement (I) and repeat the uniqueness test on (II) alone. Do not carry any fact from (I) into this pass.
Combine only after both failIf (I) already pinned the answer, stop — that is A, even if (II) also looks true. If (II) pinned it, that is B. Combining is for the both-needed and neither cases only.

The extra comparison is a decoy

Who is tallest among Priya, Rohan and Meena? (I) Priya is taller than both Rohan and Meena. (II) Rohan is taller than Meena.

(I) alone: Priya taller than both2 orders; tallest = Priya both times — I sufficient
(II) alone: Rohan > Meena3 orders; tallest = Priya or Rohan — II fails
Together (unused extra)still Priya; (II) was never needed
Code (this topic)A, not D

Pro tip. A tidy combined ranking (Priya > Rohan > Meena) is a ranking solve. Sufficiency already ended at (I).

Rahul starts facing north. After one 90° turn (left or right), which way does he face? (I) He makes a 90° turn. (II) He turns to his right. Using this topic's codes, the answer is

I alone sufficient (II not)
II alone sufficient (I not)
Both together necessary

From north, a 90° turn faces west (left) or east (right). (I) restates the turn and leaves both facings, so it fails. (II) forces a right turn: north → east, uniquely. Code B. Combining 'he turns' with 'he turns right' and bubbling both-needed is the trap — (II) already answered.

3Either means each statement already answers

Code C, 'either', is the most misread word on the paper. It does not mean 'use either statement as a clue toward a joint answer'. It means each statement, taken alone with the question, already pins one answer. If you need both of them in the same working, you are in the both-needed case, not in C.

Meena stands in a row of nine. What is her position from the left? (I) she is 4th from the left — the position is 4, done. (II) she is 6th from the right. Rank from the left equals total minus rank from the right, plus one: 9 − 6 + 1 = 4. Same unique answer, from (II) alone. You could ignore either statement and still finish. That is C.

The trap is seeing that both statements agree, feeling thorough for checking both, and bubbling D. Agreement is not the test. Independent sufficiency is the test. D is the both-needed case, where each statement still leaves a fork.

Figure. Both statement cards pin Meena's left-rank on their own (sage). Verdict is either — each alone already answers — not both-needed.

How either is decided

Ask of (I): done yet?If (I) alone pins the asked quantity, tick I-sufficient. Do not peek at (II) during this pass.
Ask of (II): done yet?If (II) alone also pins it — possibly by a different route, such as converting a right-rank with total − R + 1 — tick II-sufficient.
Two ticks is eitherC is both ticks. One tick is A or B. Zero ticks means you have not reached C; go on to both-needed versus neither.

Two independent routes to the same rank

In a row of 9, what is Meena's position from the left? (I) Meena is 4th from the left. (II) Meena is 6th from the right.

(I) 4th from the leftleft-rank = 4 — I sufficient
(II) 6th from the right; total = 9left-rank = 9 − 6 + 1 = 4 — II sufficient
Each route ignored the other statementtwo independent pins of the same 4
Code (this topic)C — either, not both-needed

Pro tip. Checking that 4 matches 4 is good hygiene. It is not a reason to bubble D. D requires that neither route worked alone.

How far is Rahul from his starting point after two walking legs? (I) He walks 5 km east then 5 km west. (II) He walks 3 km north then 3 km south. Using this topic's codes, the answer is

I alone sufficient (II not)
Either I or II alone sufficient
Both together necessary

(I) east 5 then west 5 nets 0 km, uniquely. (II) north 3 then south 3 nets 0 km, uniquely. Each statement already answers; you can ignore either one. That is C. Bubbling both-needed because the two walks agree is the 'either' trap.

4Both needed: each leaves a fork; together they pin one

Code D is the case the word 'both' actually names: statement (I) leaves at least two possible answers, statement (II) leaves at least two possible answers, and the arrangements that survive both statements together leave exactly one.

Three of the office colleagues — Priya, Rohan, Meena — stand in a line facing north. Who is in the middle? (I) Priya is at an end. Four of the six line-ups put Priya at an end, and the middle person is Rohan in two of them and Meena in the other two. (II) Meena is at the right end. Two line-ups survive: Priya–Rohan–Meena (middle Rohan) and Rohan–Priya–Meena (middle Priya). Neither statement names the middle. Together, Priya must be at an end and Meena at the right, so the only surviving line is Priya–Rohan–Meena. The middle is Rohan, uniquely. That is D.

If you skip the alone-tests and only draw the combined line, D and A look identical — you got an answer. The alone-tests are what distinguish 'I already knew' from 'I needed both facts'.

Figure. Each statement card is incomplete on its own (warm/neutral). The verdict bar is the intersection: together they pin Rohan in the middle.

Fix then intersect

Count answers under (I)List the legal line-ups (here all 6 permutations of three people). If the asked seat still has two names, (I) has failed. Do not stop drawing just because the field shrank.
Count answers under (II)Restart from all line-ups. If the asked seat still has two names, (II) has failed too.
Intersect the two listsKeep only line-ups that satisfy both statements. One leftover answer is D. Two or more leftover answers is the neither case.

Two forks, one intersection

Priya, Rohan and Meena stand in a line facing north. Who is in the middle? (I) Priya is at an end. (II) Meena is at the right end.

(I) Priya at an end — 4 line-upsmiddle = Rohan or Meena — I fails
(II) Meena at the right — 2 line-upsmiddle = Rohan or Priya — II fails
Intersection: Priya at an end and Meena at rightonly Priya–Rohan–Meena; middle = Rohan
Code (this topic)D — both together necessary

Pro tip. Four plus two is not the test. The intersection of those lists is. Here it has one line-up, so D; if it had two, the code would flip to E.

Rahul starts facing north and makes two 90° turns (each left or right). After both turns, which way does he face? (I) The first turn is to his right. (II) The second turn is to his right. Using this topic's codes, the answer is

I alone sufficient (II not)
II alone sufficient (I not)
Either I or II alone sufficient
Both together necessary
Even both together not sufficient

Four walks: LL ends south, LR north, RL north, RR south. (I) first-right keeps RL (faces north) and RR (faces south) — two facings. (II) second-right keeps LR (north) and RR (south) — two facings. Together only RR remains: north → east → south. Unique facing south. Code D.

5Neither: extra facts can still leave a branch

Code E is the honest failure: even after you use every printed fact, two legal completions still disagree on the asked quantity. Extra information is not the same as enough information.

All four colleagues line up facing north. Who is at the left end? (I) Rohan is second from the left — the left end is still Priya, Meena or Anil. (II) Meena is second from the right — the left end is still Priya, Rohan or Anil. Together the row is forced into _ Rohan Meena _, and the left end is Priya in one completion and Anil in the other. The question is still open. That is E, not D.

The trap is treating 'I used both statements' as 'both were necessary'. Necessity is D, where the intersection pins one answer. E is the leftover branch you can still see after the intersection. If two names remain, you do not guess; you bubble neither.

Figure. Both cards fill a seat and still leave the asked left end open (terracotta). Verdict is neither: the row is _ Rohan Meena _, so Priya or Anil.

Order of attack

Alone-tests firstConfirm that (I) alone leaves two or more answers and (II) alone leaves two or more. If either already pinned the question, you are not in E.
Draw the intersectionPlace every fact from both statements. Write the seats that are still free, not just the seats that filled.
Count leftover namesIf the asked seat still has two names, the code is E. Filling two other seats does not license a guess at the asked one.

Two seats filled, the asked seat still forks

Priya, Rohan, Meena and Anil stand in a line facing north. Who is at the left end? (I) Rohan is second from the left. (II) Meena is second from the right.

(I) Rohan 2nd from leftleft end in {Priya, Meena, Anil} — I fails
(II) Meena 2nd from rightleft end in {Priya, Rohan, Anil} — II fails
Together: _ Rohan Meena _left end in {Priya, Anil} — still two names
Code (this topic)E — even both together not sufficient

Pro tip. Rohan and Meena are placed. That feels like progress. The question asked for the left end, and two names still sit there — so E, not D.

Rahul starts facing north and makes two 90° turns (each left or right). After the first turn, which way does he face? (I) Exactly one of the two turns is a right turn. (II) After both turns he faces north. Using this topic's codes, the answer is

II alone sufficient (I not)
Both together necessary
Even both together not sufficient

Exactly one right turn among two 90° turns is LR (north → west → north) or RL (north → east → north). Ending facing north is the same pair. After the first turn the facing is west or east in both surviving walks. (I) fails, (II) fails, together still two facings. Code E. The statements look different and still describe the same leftover branch.

Notes

A statement is sufficient only when every legal completion of the inner puzzle gives the same answer to the question. Two remaining names, ranks or facings means the statement has failed, even if it feels helpful.
Always test statement (I) alone, then statement (II) alone, and combine only if both failed. A pair that works together often had one statement that already worked alone — that is A or B, not D.
Code C ('either') means each statement independently pins one answer. It is not a licence to mix clues from (I) and (II) in one working.
Code D needs both forks: (I) leaves two or more answers, (II) leaves two or more, and the intersection leaves exactly one. Skipping the alone-tests makes D look like A.
Code E is a leftover branch after the intersection. Using both statements is not the same as needing both; if two names remain, bubble neither, do not guess.

Formulas

A statement is sufficient iff every arrangement (or walk) consistent with it gives the same answer to the asked question.
Try (I) alone, then (II) alone, then both; never start at both.
Either (C) = each statement independently pins one answer.
Both needed (D) = each alone leaves two or more possibilities, and the intersection leaves one.
Neither (E) = the intersection still leaves two or more possibilities.

Exam traps & shortcuts

Uniqueness, not usefulness: a clue can shrink the field and still fail.
Read this paper's directions before bubbling D or E — some bank papers swap those two codes.
Enumerate the remaining possibilities on paper. If two survive, the data are not sufficient.
Do not finish a ranking or direction puzzle the question did not ask. Stop the moment the asked quantity is unique — or the moment it is not.

Reference tables

A, B and C stay put across papers. D and E are the pair some bank papers reverse. This topic uses D = both needed and E = neither.

Attack order and the D/E swap
Move	Do this
Read this paper's codes	A/B/C are stable; confirm whether D is both-needed or neither
Try (I) alone	List completions; one answer means (I) is sufficient
Try (II) alone	Same uniqueness test on (II); carry no fact from (I)
Combine only if both failed	One leftover answer = both needed; two or more = neither

Recap

Before a data-sufficiency set, hold only this.

Uniqueness: A statement suffices only when every legal completion gives the same answer. Two remaining names means failure.
Alone first: Test (I) alone, then (II) alone. Jumping to both-needed is how A and B become D.
Either: C means each statement independently pins one answer. Agreement between (I) and (II) is not D.
Both needed: D is two failed alone-tests whose intersection leaves exactly one answer.
Neither: E is a leftover branch after the intersection. Using both statements is not the same as needing both.
D/E swap: This topic uses D = both needed, E = neither. Some bank papers reverse those two. Read the directions on the paper in front of you.

Practise Reasoning Data Sufficiency

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16 exam-style questions on this topic, with explanations
A 5-question practice set that ends the chapter
Timed mocks scored with the real marking scheme
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