UGC – NET Computer Science June 2009 – Paper – II

Question 1:

If x and y are independent Gaussian random variables with average value 0 and with the same variance, their joint probability density function is given by:

• (A) p(x, y) = p(x) p(y)
• (B) p(x, y) = p(x) + p(y)
• (C) p(x, y) = p(x + y)
• (D) p(x, y) = p(x) p(y) + p(x)

Show Answer & Explanation

Correct Answer: ✅ (A) p(x, y) = p(x) p(y)

Explanation: When two random variables are independent, their joint probability density function (PDF) is the product of their individual PDFs.

Question 2:

In order that a code is ‘t’ error correcting, the minimum Hamming distance should be:

• (A) t
• (B) 2t – 1
• (C) 2t
• (D) 2t + 1

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Correct Answer: ✅ (D) 2t + 1

Explanation: The **minimum Hamming distance** required for a code to correct **t errors** is **2t + 1**.

Question 3:

The Boolean expression \( \bar{x} y + y z + y z \) is equivalent to:

• (A) x
• (B) y
• (C) z
• (D) x + y + z

Show Answer & Explanation

Correct Answer: ✅ (B) y

Explanation: Boolean simplification gives \( \bar{x} y + y z + y z = y \).

Question 4:

The characteristic equation of a JK flip flop is:

• (A) Q(n+1) = J Q(n) + K Q(n)
• (B) Q(n+1) = J Q(n) + K̅ Q(n)
• (C) Q(n+1) = Q(n) J K
• (D) Q(n+1) = (J + K) Q(n)

Show Answer & Explanation

Correct Answer: ✅ (B) Q(n+1) = J Q(n) + K̅ Q(n)

Explanation: The **characteristic equation** of a JK flip flop is derived as \( Q_{n+1} = J Q_n + \overline{K} Q_n \).

Question 5:

In order to implement an n-variable switching function, a MUX must have:

• (A) 2ⁿ inputs
• (B) 2ⁿ + 1 inputs
• (C) 2ⁿ – 1 inputs
• (D) 2ⁿ – 1 inputs

Show Answer & Explanation

Correct Answer: ✅ (A) 2ⁿ inputs

Explanation: A **Multiplexer (MUX)** requires **2ⁿ inputs** to implement an n-variable switching function.

Question 6:

The throughput of pure ALOHA is given by:

• (A) S = G
• (B) S = e²ᴳ
• (C) S = Ge²ᴳ
• (D) S = Ge⁻²ᴳ

Show Answer & Explanation

Correct Answer: ✅ (D) S = Ge⁻²ᴳ

Explanation: The throughput of pure ALOHA is given by **S = G e⁻²ᴳ**, where G is the average number of transmission attempts per frame time.

Question 7:

The Fiber Distributed Data Interface uses:

• (A) single mode fibers and LEDs
• (B) multimode fibers and LEDs
• (C) single mode fibers and ILDs
• (D) multimode fibers and ILDs

Show Answer & Explanation

Correct Answer: ✅ (B) multimode fibers and LEDs

Explanation: The **Fiber Distributed Data Interface (FDDI)** primarily uses **multimode fibers and LEDs** for optical signal transmission.

Question 8:

To employ multi-access in GSM, users are given different:

• (A) time slots
• (B) bandpass filters
• (C) handsets
• (D) frequency bands

Show Answer & Explanation

Correct Answer: ✅ (D) frequency bands

Explanation: In **GSM (Global System for Mobile Communications)**, users are given different **frequency bands** to enable multi-access and avoid interference.

Question 9:

With four programs in memory and 80% average I/O wait, the CPU utilization is:

• (A) 60%
• (B) 70%
• (C) 90%
• (D) 100%

Show Answer & Explanation

Correct Answer: ✅ (C) 90%

Explanation: Using the formula: CPU Utilization = 1 – (I/O Wait Percentage)⁴ = 1 – (0.8)⁴ = 1 – 0.4096 = **0.5904 ≈ 90%**.

Question 10:

Assume N segments in memory and a page size of P bytes. The wastage on account of internal fragmentation is:

• (A) NP/2 bytes
• (B) P/2 bytes
• (C) N/2 bytes
• (D) NP bytes

Show Answer & Explanation

Correct Answer: ✅ (A) NP/2 bytes

Explanation: The expected internal fragmentation per segment is **P/2 bytes**. Since there are **N segments**, total wastage = **N × P/2 bytes**.

Question 11:

Assertion (A): Bit maps are not often used in memory management.

Reason (R): Searching a bit map for a run of a given length is a slow operation.

• (A) Both (A) and (R) are true and (R) is correct explanation for (A)
• (B) Both (A) and (R) are true but (R) is not correct explanation for (A)
• (C) (A) is true (R) is false
• (D) (A) is false (R) is true

Show Answer & Explanation

Correct Answer: ✅ (A) Both (A) and (R) are true and (R) is correct explanation for (A)

Explanation: Bit maps are rarely used in memory management because searching for a free block of a given length is time-consuming.

Question 12:

The complete graph with four vertices has k edges where k is:

• (A) 3
• (B) 4
• (C) 5
• (D) 6

Show Answer & Explanation

Correct Answer: ✅ (D) 6

Explanation: The number of edges in a complete graph with n vertices is given by the formula n(n-1)/2. For n = 4, we get 4(3)/2 = 6.

Question 13:

The octal equivalent of hexadecimal (A.B)₁₆ is:

• (A) 47.21
• (B) 12.74
• (C) 12.71
• (D) 17.21

Show Answer & Explanation

Correct Answer: ✅ (C) 12.71

Explanation: Convert (A.B)₁₆ to binary: A = 1010, B = 1011 → 1010.1011. Convert to octal: (1010.1011)₂ = (12.71)₈.

Question 14:

A reduced state table has 18 rows. The minimum number of Flip flops needed to implement the sequential machine is:

• (A) 18
• (B) 9
• (C) 5
• (D) 4

Show Answer & Explanation

Correct Answer: ✅ (C) 5

Explanation: The number of Flip Flops required is **log₂(Number of states)**. Since **2⁵ = 32** is the smallest power of 2 that can accommodate 18 states, 5 Flip Flops are required.

Question 15:

What is the value of ‘b’ after the execution of the following code statements?

c = 10;
b = +c + c++ + +c;

• (A) 20
• (B) 22
• (C) 23
• (D) None

Show Answer & Explanation

Correct Answer: ✅ (B) 22

Explanation: – `+c` is 10 (unary plus doesn’t change the value). – `c++` uses 10 (post-increment returns the old value and then increments `c`). – `+c` now refers to 11. – So, `b = 10 + 10 + 11 = 22`.

Question 16:

Which of the following does not represent a valid storage class in ‘C’?

• (A) automatic
• (B) static
• (C) union
• (D) extern

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Correct Answer: ✅ (C) union

Explanation: The storage classes in C are `auto`, `static`, `extern`, and `register`. `union` is a data type, not a storage class.

Question 17:

The friend functions are used in situations where:

• (A) We want to have access to unrelated classes
• (B) Dynamic binding is required
• (C) Exchange of data between classes to take place
• (D) None of the above

Show Answer & Explanation

Correct Answer: ✅ (C) Exchange of data between classes to take place

Explanation: Friend functions allow one class to access the private and protected members of another, facilitating data exchange.

Question 18:

Which of the following is correct regarding DML?

• (i) DML includes a query language based on both relation algebra and tuple calculus
• (ii) DML includes a query language based on tuple calculus
• (iii) DML includes a query language based on relational algebra
• (iv) DML includes a query language based on none of the relational algebra and tuple calculus

• (A) (i) only
• (B) (ii) only
• (C) (iii) only
• (D) (iv) only

Show Answer & Explanation

Correct Answer: ✅ (A) (i) only

Explanation: Data Manipulation Language (DML) supports queries based on both relational algebra and tuple calculus.

Question 19:

Suppose it takes 100 ns to access a page table and 20 ns to access associative memory. With a 90% hit rate, the average access time equals:

• (A) 20 ns
• (B) 28 ns
• (C) 90 ns
• (D) 100 ns

Show Answer & Explanation

Correct Answer: ✅ (B) 28 ns

Explanation: The average memory access time formula: \( T = (Hit\ Rate \times T_{TLB}) + (Miss\ Rate \times (T_{TLB} + T_{PageTable})) \) \( = (0.9 \times 20) + (0.1 \times (20 + 100)) = 18 + 10 = 28\ ns \)

Question 20:

There exists a construct which returns a value ‘true’ if the argument subquery is:

• (A) empty
• (B) non-empty
• (C) in error
• (D) none of the above

Show Answer & Explanation

Correct Answer: ✅ (B) non-empty

Explanation: The `EXISTS` construct in SQL returns `TRUE` if the argument subquery returns at least one row (i.e., it is non-empty).

Question 21:

Which construct in SQL is used to test whether a subquery has any tuples in its result?

• (A) UNIQUE
• (B) EXISTS
• (C) GROUP BY
• (D) EXCEPT

Show Answer & Explanation

Correct Answer: ✅ (B) EXISTS

Explanation: The `EXISTS` construct checks whether a subquery returns any rows. If it does, it evaluates to `TRUE`.

Question 22:

ORACLE supports:

• (A) inner join and outer join only
• (B) outer join and semi join only
• (C) inner join, outer join, semi join only
• (D) inner join, outer join, semi join and anti join

Show Answer & Explanation

Correct Answer: ✅ (D) inner join, outer join, semi join, and anti join

Explanation: ORACLE supports all these joins, where an anti join retrieves rows that do not satisfy the join condition.

Question 23:

Which two of the following are equivalent for an undirected graph G?

• (i) G is a tree
• (ii) There is at least one path between any two distinct vertices of G
• (iii) G contains no cycles and has (n–1) edges
• (iv) G has n edges

• (A) (i) and (ii)
• (B) (i) and (iii)
• (C) (i) and (iv)
• (D) (ii) and (iii)

Show Answer & Explanation

Correct Answer: ✅ (B) (i) and (iii)

Explanation: A tree is an acyclic connected graph with `n-1` edges, which corresponds to statements (i) and (iii).

24. In a B tree of order m with p nodes the average number of splits is at most:

1. 
2. 
3. 
4. None

Show Answer & Explanation

Correct Answer: ✅ (2)

Explanation: In a B-tree of order m, the maximum average number of splits is determined by the number of child nodes and balancing constraints.

25. The propositional formula given by the tree is:

1. ∧ ∨ x ₂ ∨ x₁ ¬ x₁ ¬ x₁
2. ( x₂ ∨ ¬ x₂ ) ∧ ( x₁ ∨ x ₂ )
3. (¬ x ₁ ∨ x ₂ ) ∧ (¬ x ₁ ∨ x ₂ )
4. None

26. Queue is a __ list.

1. LIFO
2. LILO
3. FILO
4. FIFO

27. In a full binary tree of height k, there are __ internal nodes.

1. 2^k-1
2. 2^k-1
3. 2^k
4. 2^k+1

28. A binary tree is said to have heap property if the elements along any path :

1. from leaf to root are non–increasing
2. from leaf to root are non–decreasing
3. from root to leaf are non–decreasing
4. from root to leaf are non–increasing

29. X.25 protocol consists of :

1. Physical and Frame levels
2. Frame and Packet levels
3. Physical, Frame and Packet levels
4. None of the above

30. GSM/CDMA systems:

1. are limited to very low speed data
2. require no local loop wires
3. are predominantly used for voice
4. all of the above

31. Usually, information security in a network is achieved by:

1. Layering
2. Cryptography
3. Grade of service
4. None of the above

32. The linker:

1. is similar to interpreter
2. uses source code as its input
3. is required to create a load module
4. none of the above

33. In which addressing mode the operand is given explicitly in the instruction itself?

1. Absolute mode
2. Immediate mode
3. Indirect mode
4. Index mode

34. A compiler that runs on one machine and produces code for a different machine is called:

1. Cross compilation
2. One pass compilation
3. Two pass compilation
4. None of the above

35. Any syntactic construct that can be described by a regular expression can also be described by a:

1. Context sensitive grammar
2. Non context free grammar
3. Context free grammar
4. None of the above

36. Find the odd man out :

1. tail
2. cut
3. wart
4. sed

37. Which of the following changes permission to deny write permission to group and others ?

1. Chmod go – w filex
2. Chmod go w filex
3. Chmod go=w filex
4. None of the above

38. Variable partition memory management technique with compaction results in :

1. Reduction of fragmentation
2. Minimal wastage
3. Segment sharing
4. None of the above

39. Capability Maturity Model is meant for:

1. Product
2. Process
3. Product and Process
4. None of the above

40. In the light of software engineering software consists of :

1. Programs
2. Data
3. Documentation
4. All of the above

41. Which one of the following ISO standard is used for software process?

1. ISO 9000
2. ISO 9001
3. ISO 9003
4. ISO 9000-3

42. Which of the following is used for test data generation?

1. White Box
2. Block Box
3. Boundary value analysis
4. All of the above

43. Reverse engineering is the process which deals with:

1. Size measurement
2. Cost measurement
3. Design recovery
4. All of the above

44. The spacing between character pairs is called:

1. Kerning
2. x-height
3. intercap
4. serif

45. When compared with analog cellular systems, an advantage of digital TDMA cellular system is that:

1. it is less complicated
2. it requires less of computer memory
3. it conserves spectrum bandwidth
4. it costs less

46. E-Commerce includes :

1. B2C
2. BEB
3. CEC
4. All of the above

47. A clustering technique that permits a convenient graphical display is :

1. partition based clustering
2. probabilistic model based clustering
3. hierarchical clustering
4. agglomerative clustering

48. After sending a message ,the sender should not be able to, at a later date, deny having sent the message, is referred to as:

1. Authenticity
2. Non-Repudiability
3. Auditability
4. Repudiability

49. The device which connects dissimilar LANs of different topologies using different sets of communication protocols so that information can flow from one to another is called:

1. Router
2. Bridge
3. Gateway
4. Switch

50. We cannot delete the __ icon but we can made it invisible.

1. Recycle
2. My computer
3. Internet explorer
4. None of the above