UGC NET Computer Science PYQ, December 2014 (Paper II & III, Selected Questions)

Explanation

The Excess-3 decimal code is a self-complementing code because the binary sum of a code and its 9's complement is equal to 9 and the complement can be generated by inverting each bit pattern.

Explanation

To add two BCD digits we need two 4-bit adders: the first adds the two BCD numbers and the second corrects the result to a valid BCD number. The first 4-bit adder needs 3 full adders and 1 half adder (giving A₃ A₂ A₁ A₀). In the correction step 0110 is added to A₃ A₂ A₁ A₀. A₀ is always added to 0, so no adder is needed; A₁ is added to 1 with no incoming carry, so a half adder is used; A₂ is added to 1 plus a carry, so a full adder is used; A₃ is added only to the carry, so a half adder is used. Total = 3 + 1 = 4 full adders and 1 + 2 = 3 half adders.

Explanation

Total inputs to the ROM = 8 + 8 (two 8-bit numbers) + 1 (mode) + 1 (carry in) = 18, so the ROM has 2¹⁸ words. Outputs = 8 result bits + 1 carry out + 1 overflow = 10 bits. Hence the ROM size is 2¹⁸ × 10.

Explanation

The postfix form of the expression is AB*CD*E/+. Counting a PUSH for each of the 5 operands and a POP for each of the 4 operators (ignoring the pushes of intermediate results), the evaluation needs 5 PUSH and 4 POP instructions.

Explanation

Each cell needs 4 words. In row-major order, rows 0 to 10 contain 11 × 10 = 110 elements, and A[11][0] to A[11][4] add 5 more, so 115 elements precede A[11][5]. Address = 100 + 4 × 115 = 560.

Explanation

^ has the highest precedence, so B^D becomes BD^, and A + B^D becomes ABD^+. E – F becomes EF–. Dividing gives ABD^+EF–/, and adding G gives ABD^+EF–/G+.

Explanation

A full binary tree with n leaves contains n – 1 internal nodes, so total nodes = internal nodes + leaves = (n – 1) + n = 2n – 1.

Explanation

For a sorted list followed by a few random elements: bubble sort and selection sort take O(n²) time, quick sort degrades to its O(n²) worst case on nearly sorted input, while insertion sort takes close to O(n) time. Hence insertion sort is most suitable.

Explanation

The DES algorithm works with a 64-bit block size, employs 16 processing rounds, and is driven by a 56-bit key (with 8 additional parity bits), making up a total of 19 distinct stages.

Explanation

Probability of k = 1 in one trial = 1/1000000 = 10⁻⁶, so the probability of k ≠ 1 is 1 – 10⁻⁶. Probability that 1 is never printed in 10⁶ printouts = (1 – 10⁻⁶)^(10⁶) ≈ 1/e. Probability that 1 is printed at least once = 1 – (1 – 10⁻⁶)^(10⁶) ≈ 1 – 1/e = 0.632121.

Explanation

gof(x) = √(x⁸ + 1), so ho(gof)(x) = (x⁸ + 1) + 72 = x⁸ + 73. hog(x) = (x² + 1) + 72 = x² + 73, so (hog)of(x) = x⁸ + 73. Hence both are x⁸ + 73.

Explanation

A friend function of a class is a non-member function that is given the same access as member methods to the class's private and protected data. It is declared inside the class that grants access, but it is not a member of the class.

Explanation

x++ is a post-increment, so the old value 128 is used in the expression and printf prints 1 + 128 = 129; x becomes 129 only afterwards.

Explanation

Average internal fragmentation per process is y/2. A process has x/y pages and each page-table entry needs z bytes, so the page table takes xz/y bytes. Total overhead = xz/y + y/2. Setting d/dy (xz/y + y/2) = –xz/y² + 1/2 = 0 gives y = √(2xz).

Explanation

Average time to service a page fault = 0.7 × 20 + 0.3 × 8 = 14 + 2.4 = 16.4 m. sec.

Explanation

Two-level scheduling is used to schedule efficiently when some processes are swapped out. A lower-level scheduler (e.g. round robin) selects only among the processes in memory, while a higher-level scheduler swaps processes in and out of memory. Hence I and III are correct.

Explanation

The program text is shared, so it is not multiplied by 5. As given in the book, total memory = 200 + 15 + 50 + 70 = 335 K.

Explanation

A correct solution must not let a process running outside its critical section block other processes. So condition (c) does not hold good for a solution to the critical section problem.

Explanation

Only I is correct: a self join is implemented on a single table using alias names. Outer join is not a basic relational algebra operation, and natural join and outer join are not equivalent.

Explanation

A weak entity does not have sufficient attributes to form a primary key; it is drawn as a double rectangle in an ER diagram. A weak entity set can be converted into a strong entity set simply by adding suitable attributes.

Explanation

The candidate keys are AB, CD, BC and AD, so A, B, C and D are all prime attributes and the relation is in 3NF. It is not in BCNF because in C → A and D → B the left side is not a superkey. Hence the best normal form is 3NF.

Explanation

{A}⁺ = {A, B, C, D}, which does not include E, so A alone is not a key. {AE}⁺ = {A, B, C, D, E}, and nothing can be removed from AE, so AE is the minimal key.

Explanation

Correct match: A. Call control protocol – iii. Connection management; B. A-bis – i. Interface between BTS and BSC; C. BSMAP – iv. Works between MSC and BSS; D. CDMA – ii. Spread spectrum.

Explanation

The signal sends 2000 signal elements (baud) per second and 6000 bits per second, so each signal element carries 6000/2000 = 3 bits/baud.

Explanation

The C2B model, also called a reverse auction or demand collection model, enables buyers to name their own (often binding) price for a specific good or service. The website collects the bids and offers them to participating sellers. C2C is consumer to consumer, and B2B and B2G have nothing to do with consumer price setting.

Explanation

Inventory and data mining have nothing to do with price. Economic Order Quantity (EOQ) is the order quantity that minimizes total holding and ordering costs. The demand-sensitive pricing model brings prices down as more customers buy the product at once.

Explanation

The umbrella activities in a software development life cycle process include the following: software project management, formal technical reviews, software quality assurance and software configuration management. Umbrella activities occur throughout the software process and focus primarily on project management, tracking and control.

Explanation

Effective software metrics should be simple, computable, consistent, objective and consistent in the use of units and dimensions. They should not be programming language dependent, otherwise they cannot measure software consistently.

Explanation

Cyclomatic complexity measures the logical complexity of a program (the number of independent paths). It can be computed as: (1) the number of regions of the flow graph; (2) V(G) = E – N + 2, where E is the number of edges and N the number of nodes; (3) V(G) = P + 1, where P is the number of predicate nodes in the flow graph G.

Explanation

These process areas belong to maturity level 3 (Defined), which includes Requirements Development, Organizational Process Focus (OPF), Organizational Training (OT), Integrated Project Management (IPM) and Risk Management (RSKM).

Explanation

Software architecture is the set of significant decisions about the organization of a software system: the structural elements and their interfaces, their behaviour and collaboration, and their composition into larger subsystems.

Explanation

A computer based information system is needed because of the growing size of organizations which need to process large volumes of data, and such data must support timely and accurate decisions. So III and IV are true.

Explanation

In increasing order of access speed: Magnetic tapes < Optical disks < Magnetic (hard) disks < Electronic disks (flash/SSD) < Main memory < Cache < Registers.

Explanation

Internal interrupts occur due to internal errors (like division by zero) and external interrupts come from hardware. Software interrupts are the most appropriate way to switch from user mode to supervisor (kernel) mode.

Explanation

For any comparison-based sort the decision tree has at least n! leaves, so its height is at least lg(n!) = Ω(n lg n).

Explanation

Dijkstra's algorithm for the single-source shortest-paths problem is a greedy algorithm, and the Floyd-Warshall algorithm for all-pairs shortest paths is a dynamic programming algorithm.

Explanation

To show CLIQUE is NP-hard, a known NP-complete problem must be reduced to CLIQUE (e.g. 3-CNF-SAT ≤ₚ CLIQUE), not the other way round. Reducing CLIQUE to 3-CNF-SAT, VERTEX_COVER or SUBSET_SUM only shows CLIQUE is no harder than them. So the answer is None of the above.

Explanation

Autoboxing is the automatic conversion that the Java compiler makes from primitive types to their corresponding object wrapper classes.

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.

Explanation

Synchronization is the capability to control the access of multiple threads to shared resources. Without it, one Java thread could modify a shared variable while another thread is using or updating the same variable; synchronized methods prevent this.

Explanation

In the applet life cycle, init() is called first, followed by start(), paint(), stop() and destroy().

Explanation

Check-pointing saves a snapshot of the system state periodically, so that after a failure recovery can restart from the last checkpoint; this limits the volume of log information that has to be processed.

Explanation

Windows Vista's built-in disk management (Logical Disk Manager) supports shrinking and expanding volumes.

Explanation

Every binary relation (a relation with only 2 attributes) is always in BCNF: if both attributes form the key it is in BCNF, and if one attribute is the key the other is determined by it. So statement (a) is false.

Explanation

HDLC (High-level Data Link Control) is a bit-oriented, code-transparent, synchronous data link layer protocol from ISO. It can be used for point-to-point and point-to-multipoint links.

Explanation

Two phase locking is a pessimistic protocol (it assumes conflicts will happen) because it applies locks. Time stamping is an optimistic protocol because it uses no locking and handles conflicts later. So II and III are correct.

Explanation

A JavaScript program can define the behaviour of document elements by registering appropriate event handlers.

Explanation

Dithering approximates halftones without reducing spatial resolution. The dither matrix is treated like a floor tile that is repeatedly positioned one copy next to another to cover the entire image.

Explanation

All three categories refer to animation languages: linear-list notations (e.g. 'B rotate palm'), general-purpose languages (e.g. ASAS), and graphical languages. So the answer is None of the above.

Explanation

The pumping lemma for regular languages can only be used to prove that a language is not regular. Both L₁ (which needs to compare n and k) and L₂ (which needs to compare n and m) require unbounded counting, so neither is regular.