9 Discrete Mathematics (Computer Science) questions asked in UGC NET previous year papers, each with the correct answer and explanation. Read them free on UTpaper, or attempt the full papers as timed online tests.
Q1UGC NET Computer Science, December 2014 (Paper II & III, Selected Questions)
Consider the following statements S1, S2 and S3 :
S1 : In call–by–value, anything that is passed into a function call is unchanged in the caller's scope when the function returns.
S2 : In call-by-reference, a function receives implicit reference to a variable used as argument.
S3 : In call-by-reference, caller is unable to see the modified variable used as argument
AS3 and S2 are true
BS3 and S1 are true
CS2 and S1 are true
DS1, S2, S3 are true
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Correct answer: (C) S2 and S1 are true
Explanation
S1 is true: in call-by-value, anything passed into a function is unchanged in the caller's scope when the function returns. S2 is true: in call-by-reference the function receives an implicit reference to the argument variable. S3 is false, because in call-by-reference the caller always sees the modified value of the argument.
Q2UGC NET Computer Science, June 2015 (Paper II & III, Selected Questions)
Consider a proposition given as : "x ≥ 6, if x² ≥ 25" and its proof as :
If x ≥ 6, then x² = x . x ≥ 6 . 6 = 36 ≥ 25
Which of the following is correct w.r.to the given proposition and its proof?
(1) The proof shows the converse of what is to be proved
(2) The proof starts by assuming what is to be shown
(3) The proof is correct and there is nothing wrong
A(1) only
B(3) only
C(1) and (2)
D(2) only
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Correct answer: (C) (1) and (2)
Explanation
The proposition is "if x² ≥ 25 then x ≥ 6", but the proof assumes x ≥ 6 and derives x² ≥ 25. So the proof starts by assuming what is to be shown and actually proves the converse; the proof is not correct. Statements (1) and (2) are correct, statement (3) is not.
Q3UGC NET Computer Science, June 2015 (Paper II & III, Selected Questions)
Which of the following statement is incorrect for parallel virtual machine (PVM)?
AThe PVM communication model asynchronous blocking send, asynchronous blocking receive, and non-blocking receive function.
BMessage buffers are allocated dynamically
CThe PVM communication model assumes that any task can send a message to any other PVM task and that there is no limit to the size or number of such messages
DIn PVM model, the message order is not preserved.
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Correct answer: (D) In PVM model, the message order is not preserved.
Explanation
PVM provides fault tolerance through dynamic addition and deletion of hosts/processes, and message buffers are allocated dynamically. PVM guarantees that message order between any pair of tasks is preserved, so statement (d) is incorrect.
Q4UGC NET Computer Science, June 2016 (Paper II & III, Selected Questions)
Which of the following logic expressions is incorrect
A1 ⊕ 0 = 1
B1 ⊕ 1 ⊕ 1 = 1
C1 ⊕ 1 ⊕ 0 = 1
D1 ⊕ 1 = 0
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Correct answer: (C) 1 ⊕ 1 ⊕ 0 = 1
Explanation
With the EX-OR operation, an odd number of 1's returns 1 and an even number of 1's returns 0. XOR gives 1 only when the inputs are different (A ⊕ B = A'B + AB'). Here 1 ⊕ 1 ⊕ 0 has two 1's, so it equals 0, not 1. Therefore the incorrect expression is (c) 1 ⊕ 1 ⊕ 0 = 1.
Q5UGC NET Computer Science, June 2016 (Paper II & III, Selected Questions)
What is the value returned by the function f given below when n = 100?
int f(int n)
{ if (n == 0) then return n;
else
return n + f(n – 2);}
A2550
B2556
C5220
D5520
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Correct answer: (A) 2550
Explanation
The function is recursive and starts with n = 100. It keeps adding the present value to f(n – 2) and stops at n = 0, where it returns 0. So it computes 100 + 98 + ... + 2, an arithmetic series with 50 terms, first term 100 and last term 2.
Sum = (n/2)(a + l) = (50/2)(100 + 2) = 2550
Q6UGC NET Computer Science, June 2016 (Paper II & III, Selected Questions)
Which of the following statement (s) is/are correct with reference to curve generation?
I. Hermit curves are generated using the concepts of interpolation.
II. Bezier curves are generated using the concepts of approximation.
III. The Bazier curve lies entirely within the convex hull of its control points.
IV. The degree of Bezier curve does not depend on the number of control points.
AI, II and IV only
BII and III only
CI and II only
DI, II and III only
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Correct answer: (D) I, II and III only
Explanation
Hermite curves smoothly interpolate between key points. Bezier curves approximate their control points and lie entirely within the convex hull of the control points. The number of control points determines the degree of the Bezier polynomial, so IV is false. So the answer is option (d).
Q7UGC NET Computer Science, August 2016 (Paper II & III, Selected Questions)
What is the probability that a randomly selected bit string of length 10 is a palindrome?
A1/64
B1/32
C1/8
D1/4
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Correct answer: (B) 1/32
Explanation
In a 10-bit palindrome the first 5 bits can be chosen freely and the last 5 bits are fixed by them. So there are 2⁵ palindromes out of 2¹⁰ strings. Probability = 2⁵/2¹⁰ = 1/2⁵ = 1/32.
Q8UGC NET Computer Science, June 2017 (Paper II & III, Selected Questions)
In propositional logic if (P → Q) ∧ (R → S) and (P ∧ R) are two premises such that
(P → Q) ∧ (R → S)
P ∨ R
----------
Y
Y is the premise :
AP ∨ R
BR ∨ S
CQ ∨ R
DQ ∨ S
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Correct answer: (D) Q ∨ S
Explanation
Given premises (P → Q) ∧ (R → S) and (P ∨ R). (P → Q) = ¬P ∨ Q and (R → S) = ¬R ∨ S. Resolving with P ∨ R, ¬P with P and ¬R with R resolve out, leaving the disjunction Q ∨ S (constructive dilemma). So Q ∨ S is correct.
Q9UGC NET Computer Science, November 2017 (Paper II & III, Selected Questions)
How to use these UGC NET Computer Science questions
Every question here was asked in a real UGC NET paper; the paper and shift are shown on the card, and the number opens the question on its own page. Try each one before tapping Show answer, then attempt the full UGC NET papers as timed tests to check your speed under exam conditions.