GATE 2018 CS question paper PDF and answer key

The official GATE 2018 Computer Science & Information Technology paper, organised by IIT Guwahati: 65 questions for 100 marks in 3 hours. Download the official question paper and answer key as PDFs. Below is how the marks were split by topic, the complete official answer key and 5 questions solved step by step.

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Question paper (PDF)Official answer key (PDF)

Source: the official paper and answer key published by IIT Guwahati for GATE 2018. Spotted a mistake? Email team@lemyte.com.

General Aptitude: 10 · 15 marks
Computer Science & Information Technology: 55 · 85 marks
MCQ / MSQ / NAT: 41 / 0 / 24
Marks to all: None

Not in 2027 1 question (Q 25) is on topics removed from the GATE 2027 syllabus. They are marked in the answer key below. What changed for CS

Where the marks were

GATE 2018 CS topic-wise marks

Computer Science & Information Technology questions only; General Aptitude adds 15 marks on top. The top three topics carried 32 of the 85 subject marks.

Topic	Questions	Marks
Programming and Data Structures	8	12
Computer Organization and Architecture	7	11
Discrete Mathematics	6	9
Theory of Computation	5	8
Operating System	5	8
Algorithms	4	8
Computer Networks	5	7
Databases	4	6
Compiler Design	3	5
Digital Logic	3	4
Linear Algebra	2	3
Probability and Statistics	2	3
Calculus	1	1

Free solved questions

5 solved questions from GATE 2018 CS

Question text and figures as in the official paper, the answer from the official key, and a worked solution. The other 60 solutions are in your report after you take the paper.

Q6 · General Aptitude · MCQ · 2 marks

A six sided unbiased die with four green faces and two red faces is rolled seven times. Which of the following combinations is the most likely outcome of the experiment?

(A)
Three green faces and four red faces.
(B)
Four green faces and three red faces.
(C)
Five green faces and two red faces.
(D)
Six green faces and one red face.

Answer (official key): C

Solution

Probability of getting a green face is:

p=\frac{4}{6}=\frac{2}{3}.

The number of green outcomes in 7 rolls follows a binomial distribution:

X\sim \operatorname{Binomial}\left(7,\frac{2}{3}\right).

The most likely number of green outcomes is the mode:

\left\lfloor (n+1)p \right\rfloor = \left\lfloor 8\cdot\frac{2}{3} \right\rfloor = 5.

So the most likely outcome is five green faces and two red faces.

Therefore, the correct answer is Option C.

Q7 · General Aptitude · MCQ · 2 marks

In the figure below, $\angle DEC + \angle BFC$ is equal to ____________.

Geometry figure for Q9

(A)
∠BCD − ∠BAD
(B)
∠BAD + ∠BCF
(C)
∠BAD + ∠BCD
(D)
∠CBA + ∠ADC

Answer (official key): A

Solution

From the figure:

$A, D, E$ lie on one straight line.
$E, C, B$ lie on one straight line.
$D, C, F$ lie on one straight line.
$A, B, F$ lie on one straight line.

Using angle chasing on the two intersecting transversals, the angle between $CD$ and $CB$ , namely $\angle BCD$ , can be decomposed as:

\angle BCD = \angle BAD + \angle DEC + \angle BFC.

Therefore,

\angle DEC + \angle BFC = \angle BCD - \angle BAD.

Hence, the correct answer is Option A.

Q45 · Discrete Mathematics · MCQ · 2 marks

Consider the first-order logic sentence

\varphi \equiv \exists s\exists t\exists u\forall v\forall w\forall x\forall y\ \psi(s,t,u,v,w,x,y)

where $\psi(s,t,u,v,w,x,y)$ is a quantifier-free first-order logic formula using only predicate symbols, and possibly equality, but no function symbols. Suppose $\varphi$ has a model with a universe containing 7 elements.

Which one of the following statements is necessarily true?

(A)
There exists at least one model of $\varphi$ with universe of size less than or equal to 3.
(B)
There exists no model of $\varphi$ with universe of size less than or equal to 3.
(C)
There exists no model of $\varphi$ with universe of size greater than 7.
(D)
Every model of $\varphi$ has a universe of size equal to 7.

Answer (official key): A

Solution

The formula has three existentially quantified variables:

\exists s\exists t\exists u

followed by universal quantifiers. Since there are no function symbols, if the formula has a model, it has a submodel generated by the witnesses assigned to $s,t,u$ .

At most three distinct elements are needed for these witnesses. The predicate interpretations can be restricted to this smaller universe.

Therefore, if $\varphi$ has a model of size 7, then it has a model of size at most 3.

The correct answer is Option A.

Q51 · Theory of Computation · Numerical · 2 marks

Given a language $L$ , define $L^i$ as follows:

L^0=\{\epsilon\}

L^i = L^{i-1}\cdot L \quad \text{for all } i>0.

The order of a language $L$ is defined as the smallest $k$ such that

L^k=L^{k+1}.

Consider the language $L_1$ over alphabet $\{0\}$ accepted by the following automaton.

Automaton for Q52

The order of $L_1$ is __________.

Answer (official key): 2

Solution

From the automaton, the accepted language is:

L_1=\{\epsilon\}\cup\{0^{2k+1}\mid k\ge0\}.

So $L_1$ contains the empty string and all odd-length strings over the single-symbol alphabet $\{0\}$ .

Now,

L_1^1=L_1.

But

L_1^2

contains:

$\epsilon$ ,
all odd lengths, from $\epsilon$ concatenated with odd strings,
all positive even lengths, from odd length concatenated with odd length.

Therefore,

L_1^2=\{0\}^*.

Once we reach $\{0\}^*$ , multiplying by $L_1$ again does not change the language:

L_1^2=L_1^3.

Hence the smallest such $k$ is:

2.

Therefore, the answer is 2.

Q52 · Digital Logic · Numerical · 2 marks

Consider the minterm list form of a Boolean function $F$ given below.

F(P,Q,R,S)=\sum m(0,2,5,7,9,11)+d(3,8,10,12,14)

Here, $m$ denotes a minterm and $d$ denotes a don't care term.

The number of essential prime implicants of the function $F$ is __________.

Answer (official key): 3

Solution

The ON-set is:

\{0,2,5,7,9,11\}

and the don't-care set is:

\{3,8,10,12,14\}.

Using a Karnaugh map or prime-implicant table, the prime implicants include groups that uniquely cover the minterms:

These minterms are each covered by only one prime implicant, so their corresponding prime implicants are essential.

Therefore, the number of essential prime implicants is:

3.

So the answer is 3.

The other 60 questions are solved in your report when you take GATE 2018 CS as a 3-hour test.

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Official answer key

GATE 2018 CS answer key

All 65 answers from the official key. Numerical answers are ranges; “or” means the key accepts either answer.

Download the official GATE 2018 CS answer key (PDF)

Q	Topic	Type	Marks	Answer
1	Verbal Aptitude	MCQ	1	B
2	Quantitative Aptitude	MCQ	1	B
3	Verbal Aptitude	MCQ	1	A
4	Quantitative Aptitude	MCQ	1	D
5	Quantitative Aptitude	MCQ	1	C
6	Quantitative Aptitude	MCQ	2	C
7	Spatial Aptitude	MCQ	2	A
8	Quantitative Aptitude	MCQ	2	B
9	Quantitative Aptitude	MCQ	2	B
10	Quantitative Aptitude	MCQ	2	C
11	Programming and Data Structures	Numerical	1	4
12	Linear Algebra	Numerical	1	3
13	Theory of Computation	MCQ	1	B
14	Digital Logic	MCQ	1	D
15	Databases	MCQ	1	A
16	Computer Networks	MCQ	1	C
17	Computer Organization and Architecture	MCQ	1	A
18	Discrete Mathematics	MCQ	1	D
19	Programming and Data Structures	Numerical	1	4
20	Computer Organization and Architecture	Numerical	1	59 to 60
21	Programming and Data Structures	MCQ	1	B
22	Compiler Design	MCQ	1	B
23	Databases	MCQ	1	D
24	Theory of Computation	MCQ	1	D
25	Computer NetworksNot in GATE 2027 syllabus: UDP	MCQ	1	C
26	Computer Networks	Numerical	1	34 to 35
27	Discrete Mathematics	Numerical	1	42
28	Operating System	MCQ	1	B
29	Probability and Statistics	Numerical	1	0.021 to 0.024
30	Programming and Data Structures	MCQ	1	A
31	Operating System	Numerical	1	2
32	Computer Organization and Architecture	MCQ	1	D
33	Calculus	Numerical	1	0.27 to 0.3
34	Digital Logic	Numerical	1	2
35	Discrete Mathematics	Numerical	1	3
36	Algorithms	MCQ	2	C
37	Theory of Computation	MCQ	2	D
38	Compiler Design	MCQ	2	A
39	Programming and Data Structures	MCQ	2	B
40	Compiler Design	MCQ	2	D
41	Theory of Computation	MCQ	2	B
42	Programming and Data Structures	MCQ	2	A
43	Computer Organization and Architecture	MCQ	2	C
44	Operating System	MCQ	2	C
45	Discrete Mathematics	MCQ	2	A
46	Operating System	MCQ	2	A
47	Linear Algebra	MCQ	2	D
48	Computer Organization and Architecture	MCQ	2	B
49	Algorithms	MCQ	2	A
50	Discrete Mathematics	MCQ	2	D
51	Theory of Computation	Numerical	2	2
52	Digital Logic	Numerical	2	3
53	Algorithms	Numerical	2	16
54	Computer Networks	Numerical	2	144
55	Computer Organization and Architecture	Numerical	2	32
56	Computer Networks	Numerical	2	50
57	Databases	MCQ	2	C
58	Discrete Mathematics	Numerical	2	109
59	Databases	MCQ	2	B
60	Algorithms	Numerical	2	4
61	Probability and Statistics	Numerical	2	0.6 to 0.62
62	Computer Organization and Architecture	Numerical	2	219
63	Programming and Data Structures	Numerical	2	10230
64	Operating System	Numerical	2	85
65	Programming and Data Structures	Numerical	2	80

Questions about GATE 2018 CS

How many questions are in the GATE 2018 CS paper?

65 questions for 100 marks: 10 General Aptitude questions worth 15 marks and 55 Computer Science & Information Technology questions worth 85 marks. By type, there were 41 MCQs, 24 numerical answer (NAT) questions. The paper lasted 3 hours.

Is there negative marking in GATE 2018 CS?

Yes, for MCQs only. A wrong MCQ answer costs one-third of its marks (−⅓ for a 1-mark question, −⅔ for a 2-mark question). MSQ and numerical (NAT) questions have no negative marking, and an MSQ earns marks only when every correct option is chosen.

Which topics carried the most marks in GATE 2018 CS?

Outside General Aptitude, the biggest topics were Programming and Data Structures (12 marks), Computer Organization and Architecture (11 marks), Discrete Mathematics (9 marks). The full topic-wise split is in the table on this page.

Were any GATE 2018 CS questions awarded marks to all?

No. Every question was graded with the answer in the official key.

Where does this GATE 2018 CS answer key come from?

From the official answer key published by IIT Guwahati, which organised GATE 2018. Range answers for numerical questions and questions with more than one accepted answer are kept exactly as the key gives them.

GATE 2018 CS question paper PDF and answer key

GATE 2018 CS topic-wise marks

5 solved questions from GATE 2018 CS

GATE 2018 CS answer key

Questions about GATE 2018 CS

How many questions are in the GATE 2018 CS paper?

Is there negative marking in GATE 2018 CS?

Which topics carried the most marks in GATE 2018 CS?

Were any GATE 2018 CS questions awarded marks to all?

Where does this GATE 2018 CS answer key come from?

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