UGC NET Computer Science PYQ, June 2017 (Paper II & III, Selected Questions)

Explanation

(0.4051)₈ = 0×8⁰ + 4×8⁻¹ + 0×8⁻² + 5×8⁻³ + 1×8⁻⁴ = 0 + 0.5 + 0 + 0.009765625 + 0.000244140625 = (0.510009765625)₁₀ ≈ 0.5100098

Explanation

(2357)₈ = (010 011 101 111)₂. Grouping into 4 bits from right to left: 0100 1110 1111, so it is (4EF)₁₆.

Explanation

Let x = 2³ = 8 = 1000; then x – 1 = 7 = 0111. Now x & (x – 1) = 0000 (& is bitwise AND: a result bit is 1 only if both compared bits are 1, otherwise 0). So for any power of 2 the result is all zeros.

Explanation

For a 3-bit down counter using J-K flip-flops (in toggle mode): J₀ = K₀ = 1, J₁ = K₁ = Q₀' and J₂ = K₂ = Q₁' Q₀'. So II, IV and VI.

Explanation

Absurd means utterly or obviously senseless, illogical or untrue, i.e. contrary to all reason or evident truth (A–i). Ambiguous means open to more than one meaning or interpretation (B–ii). Axiom is a self-evident truth that requires no proof, a universally accepted principle (C–iii). Conjecture is an opinion or theory formed without sufficient evidence, e.g. based on past experience (D–iv).

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.

Explanation

F₀₀(0) = 1, F₀₀(1) = 1. F₀₀(2) = (10*1 + 100)/1 = 110, F₀₀(3) = (10*110 + 100)/1 = 1200, F₀₀(4) = (10*1200 + 100)/110 = 110, F₀₀(5) = (10*110 + 100)/1200 = 1, F₀₀(6) = (10*1 + 100)/110 = 1, and the values repeat. So the set of values is (1, 110, 1200).

Explanation

By Dirac's theorem, deg(v) ≥ n/2 for every vertex; by Ore's theorem, deg(v) + deg(w) ≥ n for every pair of non-adjacent vertices v and w; and a graph with |E(G)| ≥ (1/2)(n – 1)(n – 2) + 2 edges is Hamiltonian. So all of the above.

Explanation

AX consists of AH and AL. mov al, 15 → AX = 000FH mov ah, 15 → AX = 0F0FH xor al, al → AX = 0F00H mov cl, 3 → AX = 0F00H, CL = 03 shr ax, cl → AX = 01E0H (shift right 3 times) add al, 90H → AX = 0170H, carry = 1 adc ah, 0 → AX = 0270H (adds the carry) So AX = 0270H.

Explanation

(AL) = 3AH = 00111010, (BL) = 49H = 01001001. AL – BL = 11110001, so (AL) = F1H, CF = 1, SF = 1. The carry (borrow) flag is set since the first operand is less than the second; the result is negative, so the sign flag is set.

Explanation

Statement B is false: breadth-first search can be used to find the connected components of a graph, just like depth-first search. Optimal binary search tree construction is a well-known dynamic programming application, and given only the prefix and postfix walks of a binary tree, the tree cannot be reconstructed uniquely.

Explanation

Let Xᵢ = 1 if key x collides with the i-th other key, else 0. For a universal hash family, a given pair collides with probability 1/m, so E(Xᵢ) = 1/m. Summing over the other (n – 1) keys, the expected number of collisions involving x is (n – 1)/m. Since n ≤ m, this is less than 1.

Explanation

In a sorted array, insertion and deletion take O(n) in the worst case (elements must be shifted), while the minimum and maximum are always at the two ends, so finding them takes O(1).

Explanation

Data pointer = child pointer + search field value = 7 + 14 = 21 bytes. Maximum number of entries = 1 KB/21 bytes = 1024/21 ≈ 48.76. The book picks 16 since all other options are greater than 48.

Explanation

(A) fails the max-heap property (4 has child 8). (B) is a valid max heap because every parent ≥ its children. (C) fails (1 has child 7). (D) fails (3 has children 9 and 10; 4 has child 8; 1 has child 7).

Explanation

(i) Multiples of 6 between 1 and 100 = ⌊100/6⌋ = 16 (the book counts 16 for 0 to 100). (ii) Multiples of 6 between 0 and 34 = ⌊34/6⌋ + 1 (for 0) = 5 + 1 = 6.

Explanation

p+[3–5]*[xyz] = one or more p, then any number of 3, 4 or 5, then exactly one of x, y, z. (I) p443y → matched (II) p6y → not matched, since 6 cannot be used (III) 3xyz → not matched, string must start with p (IV) p35z → matched (V) p353535x → matched (VI) ppp5 → not matched, string must end with x, y or z

Explanation

Statement I is true: a linker combines several object modules into a single load module. Statement II is wrong: a linker replaces symbolic references by addresses (it generates relocatable addresses), not absolute references by symbolic ones.

Explanation

Initial value S = 1. (1) P2 needs to access: S = 0 (no one waiting) (2) P1 needs to access: S = –1 (one process waiting) (3) P3 needs to access: S = –2 (two processes waiting) (4) P2 exits critical section: S = –1 (one process waiting) (5) P1 exits critical section: S = 0 (no process waiting)

Explanation

TLB hit ratio 70%, TLB search 30 ns, memory access 90 ns. On a hit, the page is found in the TLB (30 ns); on a miss, the TLB is searched and the page table read from memory (30 + 90 ns); then 90 ns to access the data. Total = (0.7 × 30) + (0.3 × (90 + 30)) + 90 = 21 + 36 + 90 = 147 ns

Explanation

The correct match: A. Device controller – i. Extracts information from the controller register and stores it in data buffer; B. Device driver – iii. Performs data transfer; C. Interrupt handler – iv. Processing of I/O request; D. Kernel I/O subsystem – ii. I/O scheduling.

Explanation

(1) First come – first served – No starvation (2) Round robin – No starvation (3) Priority – starvation if higher priority process called again & again lower priority starves (4) Shortest process next = starvation possible (5) Shortest remaining time first = starvation possible

Explanation

A distributed operating system is usually defined as running on more loosely coupled hardware. There is no shared memory, but provides a single memory by tightly coupled software.

Explanation

The practice of examining large pre-existing databases in order to generate new information is data mining. It refers loosely to the process of semi-automatically analyzing large databases to find useful patterns.

Explanation

(1) ERP automates and integrates majority of business – true (2) ERP provides access to information in a real time environment – true (3) ERP is inexpensive to implement – false

Explanation

CHAR and VARCHAR are both declared with a maximum length, but a CHAR column is fixed to the declared length (padded with spaces), while VARCHAR(20) uses only as much space as the stored value. So A ('Ram') needs 3 spaces and B ('Sita') needs 20.

Explanation

An instructor Id. No. cannot be null when it is the primary key – valid integrity constraint. No two citizens have the same Aadhaar-Id – valid. But 'the budget of a company must be zero' is not a valid integrity constraint. So (A) and (B) are true and (C) is false.

Explanation

Two tables are created for entities M and N, and a third table for the many-to-many relationship R₂. R₁ (one-to-many) needs no separate table: the primary key of the 'one' side is placed as a foreign key in the 'many' side. So the minimum is 3 tables.

Explanation

With R(MNPQ), M → N and P → Q, the decomposition into R₁(MN) and R₂(PQ) clearly preserves both dependencies, but it is not lossless because R₁ and R₂ have no common attribute, so R cannot be recovered by joining them.

Explanation

The correct match: A. Application layer – iv. HTTP; B. Transport layer – i. TCP; C. Network layer – ii. IP; D. Datalink layer – iii. PPP.

Explanation

Default gateway serves an access point or IP router that a networked uses to send information to a computer in another network or the internet. Default simply means that this gateway is used by default, unless an application specifies another gateway.

Explanation

A distance vector routing protocol requires that a router inform its neighbors about its topology changes periodically.

Explanation

Software engineering is an engineering discipline that is concerned with all aspects of software production.

Explanation

This model allows for the creation of a preliminary version (prototype) of the software, which can be refined iteratively based on user feedback until satisfactory version is achieved. Clarifies Requirements– The prototyping process helps customers visualize and understand what the final product will look like and how it will function. Reduce Risk– By identifying potential issues early on through prototyping, developers can avoid costly rework and delays later in the development cycle.

Explanation

Mccalls's software quality factors. (1) ability to undergo change (2) Adaptability to new environments (3) Operational characteristics but production costs & scheduling is not the aspect of quality factor.

Explanation

S1 and S2 swap the definitions: cohesion measures how well the things grouped in a module belong together, and coupling measures the degree of interaction between modules. S3 is true: if coupling is low and cohesion is high, it is easier to change one module without affecting others.

Explanation

In object-oriented programming, the decorator pattern (also known as wrapper) is a design pattern that allows behaviour to be added to an individual object, statically or dynamically at run-time, without affecting the behaviour of other objects of the same class.

Explanation

extern declares variables/functions with external linkage, giving them global visibility across files. It is the default storage class of all global variables and functions.

Explanation

Structure reference refers to the dot operator (.), which is one of the operators that cannot be overloaded in C++. The other options (>>=, unary & and unary *) can be overloaded for custom types in C++.

Explanation

A header file cannot be passed to a function in C++, while a constant, a structure and an array can be passed to a function.

Explanation

When you call an overloaded function, the compiler determines the most appropriate definition to use by comparing the arguments types you used to call the function with the parameter types specified in the definitions. The process of selecting the most appropriate overloaded function is called overload resolution.

Explanation

In a microprogrammed control unit, the next address generator (sequencer) supplies the address to the control address register (B), which addresses the control memory (C); the control word read from control memory supplies the next address information. So B is the control address register and C is the control memory.

Explanation

The '5' in 8085 indicates that it uses a single +5 V power supply (by using depletion-mode transistors), rather than the +5 V, –5 V and +12 V supplies needed by the 8080. Its clock speed is 3 MHz.

Explanation

LXI rp, data (load register pair immediate) loads a register pair with 2 bytes of immediate data. It is generally used to load SP or a memory pointer; the pairs used are H-L, D-E and B-C, where B, D, H hold the MSB and C, E, L hold the LSB.

Explanation

A binary tree of height h has at most 2ʰ leaves. Sorting n elements requires at least n! leaves, so n! ≤ 2ʰ, giving h ≥ lg(n!) ≥ (n/2) lg(n/2) = Ω(n lg n).

Explanation

Red-black trees are one of many search tree schemes that are 'balanced' in order to guarantee that basic dynamic-set operations take O(lg n) time in the worst case.

Explanation

Dijkstra's algorithm always chooses the closest vertex in V – S to add to the set S, where S is the set of vertices whose final shortest-path weights from the source are known. So it is a greedy algorithm.

Explanation

In transportation table: (i) An even number of atleast 4 cells must participate in closed loop and an occupied cell can be considered only once and not more. (ii) Closed loop may or may not be square or rectangle in shape. (iii) All cells in the loop that have a plus or minus sign, except the starting cell, must be occupied.

Explanation

(A) Strings with an even number of a's is regular, since a finite automaton can accept it. (B) Strings of a's whose length is prime, (C) palindromes over {a, b} and (D) strings of a's whose length is a perfect square are not regular: no finite automaton can accept them (provable with the pumping lemma).

Explanation

The book's solution: encapsulation allows us to focus on what something does without considering the complexities of how it works, and abstraction allows us to consider complex ideas while ignoring irrelevant details that would confuse us. Hence, as per the book, neither statement is correct.

Explanation

A class declared abstract cannot be instantiated; it must be extended and its methods implemented. It is designed only to act as a base class to be inherited by other classes. So both I and II are true.

Explanation

(A) is true by De Morgan's law: A ∩ B = (A' ∪ B')'. (B) is false: recursively enumerable languages are closed under union and intersection but not under complementation.

Explanation

CBSE(60) → CBSE(70) → CBSE(80) → CBSE(90) → CBSE(100). CBSE(100) returns 99; then CBSE(90) returns 98, CBSE(80) returns 97, CBSE(70) returns 96 and CBSE(60) returns 95. So the program prints 95.

Explanation

The loop copies all values of 'array' into p. After q = p, q refers to the same array object as p, so p[4] = 20 also makes q[4] = 20. 'array' itself is unchanged, so array[4] = 18. The output is 18 : 20.

Explanation

(i) MS-DOS was a single-user operating system. (ii) XENIX has always been multi-user. (iii) OS/2 does not provide a multi-user facility. The book's key is (d): (A), (B) and (C).

Explanation

Logical address space = number of pages × page size = 2⁶ × 2⁹ = 2¹⁵, so the logical address needs 15 bits. Physical address space = number of frames × page size = 2⁵ × 2⁹ = 2¹⁴, so the physical address needs 14 bits.

Explanation

Fair-share scheduling is a scheduling algorithm in which CPU usage is equally distributed among system users or groups, rather than equally among processes. The priority considers processor utilization by the individual process, by the user or group, and the weight assigned to the user or group, so (A), (B) and (C).

Explanation

User level threads – advantages: thread switching does not require kernel mode privileges; they can run on any OS; they are fast to create and manage. Disadvantages: in a typical OS most system calls are blocking, so if one user level thread executes a system call, all threads of that process are blocked; and a multithreaded application cannot take advantage of multiprocessing.

Explanation

'init' (PID 1) is not the first process in the system; it is the second, since the scheduler/swapper process (PID 0) is created first. So statement (c) is not correct.

Explanation

A synchronous interrupt is one whose source is in phase with the system clock, i.e. interrupts that depend on the system clock (example: a time service that uses the system clock).

Explanation

Virtual memory maps the virtual addresses used by a program into physical addresses. It provides more addressable memory, allows programs larger than physical memory to run, and allows easy swapping; it does not require more I/O. So 'More I/O is required' is incorrect.

Explanation

No single attribute determines all others. The closure {AB}⁺ = {A, B, C, D}, so AB is the only candidate key. 2NF requires non-prime attributes to be fully dependent on the key, but C depends on A alone and D on B alone (partial dependencies). So R is in 1NF but not in 2NF.

Explanation

The correlated subquery computes the average salary of the employee's own company (T.company_name = S.company_name). The query does not use max, so it does not select only the highest paid employee; it selects all employees who earn more than the average salary of their company.

Explanation

Super key: a set of attributes that uniquely identifies a tuple. Candidate key: a minimal super key (no proper subset is a super key). Primary key: the candidate key chosen to identify tuples. So Primary key ⊆ candidate key ⊆ super key.

Explanation

Regression testing verifies that previously developed and tested software still performs correctly after it is changed, so I is true. Equivalence partitioning is a black-box (not white-box) testing method, so II is false.

Explanation

Top-down testing proceeds from the main module to sub-modules; a sub-module not yet developed is simulated by a temporary program called a STUB. Bottom-up testing proceeds from sub-modules to the main module, using DRIVERS to simulate the main module. So only I is true.

Explanation

Vertical alignment of table contents is set by <td valign = 'top | middle | bottom | baseline'> Text here </td>. No option matches exactly; taking 'centre' as middle, option (b) matches.

Explanation

I is false: XML tags are case-sensitive. II is true: JavaScript identifiers are case-sensitive. III is false: CSS can be applied to any XML document. IV is false: a well-formed XML document does not need a DTD. (The book keys option (d).)

Explanation

A GKS segment is any object described by GKS commands and data that start with CREATE SEGMENT and terminate with CLOSE SEGMENT. Segments allow objects to be manipulated by simply referring to the segment number, so segments can be translated, rotated, panned and zoomed.

Explanation

Multilayer perceptron network and support vector machines are examples of supervised learning, while self organizing feature maps and Hopfield networks are examples of unsupervised learning.

Explanation

From α ⊃ β and α infer β is Modus Ponens (not Modus Tollens), and Modus Tollens infers ¬α from α ⊃ β and ¬β. R2 is not Modus Ponens either. So neither R1 nor R2 is correct.

Explanation

A planning graph consists of a sequence of levels that correspond to time steps in the plan; level 0 is the initial state. Each level contains a set of literals (all that could be true at that time step) and a set of actions (all whose preconditions could be satisfied at that step). It is used to obtain heuristic estimates, and a solution can be extracted using GRAPHPLAN.

Explanation

Game playing uses heuristic search, since brute-force computation over hundreds of thousands of positions is not practical.

Explanation

Deterministic and non-deterministic pushdown automata have different expressive power (NPDA accept all context-free languages, DPDA only deterministic CFLs). DFA and NFA are equivalent, and all the Turing machine variants are equivalent.