isro cs question paper solution 2018 Q61 Set-A

The Operating System of a computer may periodically collect all the free memory space to form contiguous block of free space. This is called

(a) Concatenation
(b) Garbage collection
(c) Collision
(d) Dynamic memory allocation

Correct Answer: ?? 

isro cs question paper solution 2018 Q59 Set-A

The lower degree of cohesion is kind of

(a) logical cohesion
(b) Coincidental cohesion
(c) Procedural cohesion
(d) Communicational Cohesion

Correct answer: (b) Coincidental cohesion

Coincidental cohesion (lowest cohesion)
Logical cohesion
Temporal cohesion
Procedural cohesion
Communicational cohesion
Sequential cohesion
Functional cohesion (highest cohesion)

isro cs question paper solution 2018 Q57 Set-A

Given a binary-max heap. The elements are stored in an array as 25, 14, 16, 13, 10, 8,12. What is the content of the array after two delete operation.

(a) 14, 13, 8, 12, 10

(b) 14, 12, 13, 10, 8

(c) 14, 13, 12, 8, 10

(d) 14,13, 12, 10, 8

Correct answer: (d) 14,13, 12, 10, 8

max hip has the root value greater that it's child nodes.

Delete operation in max heap will delete the root node value. After deletion of root, node with larger value out of its two child nodes will become root as shown below.

max heap stored in array as you traverse the heap in breadth first search way.

Initially, array has values [25,14,16,13,10,8,12] -- after deletion array has values [14,13,10,8,12].

means two larger values deleted and largest value after that becomes root. 

isro cs question paper solution 2018 Q19 Set-A

Given √224_r = 13_r  the value of radix r is

(a) 10
(b) 8
(c) 6
(d) 5

Correct answer is:  (d) 5

for radix r =10,  13 is not the root of 224
for radix r =8,  224r = (64*2+8*2+4) =128+20 =148 is not a perfect square
for radix r =6,  224r = (36*2+6*2+4) =72+16 =88 is not a perfect square
for radix r =5, 224r = (25*2+5*2+4) =50+14 =64 is a perfect square.So, square root of 64 =8 =(13)₅ 

isro cs question paper solution 2018 Q62 Set-A

❔ Any set of Boolean operators that is sufficient to represent all Boolean expressions is said to be complete. Which of the following is not complete ?

(a) {AND, OR}
(b) {AND, NOT}
(c) {NOT, OR}
(d) {NOR}

Correct Answer is: (a) {AND, OR}

other options
(b) {AND, NOT} - forms NAND gate
(c) {NOT, OR}     - forms NOR gate
(d) {NOR} - (NOR and NAND gates are universal/complete)

isro cs question paper solution 2018 Q74 Set-A

 Avalanche Effect in Cryptography

(a) Is desirable property of cryptographic algorithm
(b) Is undesirable property of cryptographic algorithm
(c) Has no effect on encryption algorithm.
(d) None of above

Correct Answer is: (a)
Avalanche effect is drastic change in the cipher-text with small changes( e.g. change of a bit from 0 to 1) in either plain-text or key used for encryption/hashing.

https://en.wikipedia.org/wiki/Avalanche_effect

isro cs question paper solution 2018 Q6 Set-A

A data driven machine is one that executes an instruction if the needed data is available. The physical ordering of the code listing does not dictate the course of execution. Consider the following pseudo-code

(A) Multiply E by 0.5  to get F
(B) Add A and B to get E
(C) Add B with 0.5 to get D
(D) Add E and F to get G
(E) Add A with 10.5 to get C

Assume A,B,C are assigned values and the desired output is G. Which of the following sequence of execution is valid?

(a) B, C, D, A, E
(b) C, B, E, D, A
(c) A, B, C, D, E
(d) E, D, C, B, A

Correct Answer is:

E*0.5 = F
A+B=E
B+0.5==D
E+F=G
A+10.5=C

As execution is based on availability values for variables (A,B,C,D,E):

G is the output
So,
E+F=G (requires the E and F computed before this operation)

E and F computed in step (B) and (A) of the execution list (E and F are not assigned any values at start of the execution).

So, Step (B) and step (A) should be completed before step (D).

As the option (c) is satisfying the order. 

isro cs question paper solution 2018 Q5 Set-A

Question 5

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Consider the following table in a relational database

Last Name	Rank	Room	Shift
Smith	Manager	234	Morning
Jones	Custodian	33	Afternoon
Smith	Custodian	33	Evening
Doe	Clerical	222	Morning

According to the data shown in the table, which of the following could be a candidate key of the table?

(a) { Last Name}

(b) { Room }

(c) { Shift }

(d) { Room, Shift }

Correct answer:  (d) { Room, Shift }

Explanation: 

Candidate key is the attribute or set of attribute which uniquely identifies the tuple.  

Smith not uniquely identifies the tuple: as Smith-> manager (Rank) and Smith-> Custodian (Rank).

Similarly, Room gives different Shift value for key 33 (Room).

Similarly, Shift gives different Room value for key Morning (Shift).

So, after combining the { Room, Shift } as a candidate key to uniquely identify the tuples.

isro cs question paper solution 2018 Q4 Set-A

❔ The following C program

main()
{
fork(); fork(); printf("yes");
}

If we execute this core segment, how many times string yes will be printed ?

(a) only once
(b) 2 times
(c) 4 times
(d) 8 times

Correct answer: (c) 4 times  ==>  two fork call will produce total  ((2^2) -1) = 3  new processes and the one main(initial) process  == 4 process after 2nd fork call.

lets say Starting process is P1 then after fork() call new process P2 generated,

Now, two processes are running P1 and P2. After second fork call the P1, P2 produces two new process P3 and P4. So total processes is 4. So, each process now executes the statement - "printf("yes")"

isro cs question paper solution 2018 Q3 Set-A

❔ If a variable can take integral values from 0 to N, where N is an integer, then the variable can be represented as a bit-field whose width is (the log in the answers are to the base 2, and [logN] means the floor of logN)

(a) [log N] +1 bits
(b) [log(N-1)]+1 bits
(c) [log(N+1)]+1 bits
(d) None of the above

Correct Answer is (a) [log N] +1 bits

Consider the number 128

then, we requires the log[128] +1 == 8 bits required.

for, n=128, the option (b) doesn't satisfy ==> log (floor(128-1)) +1 = between(6 to 7)+1=6+1= 7

now take 127 then option (c) doesn't not satisfy==> log[127+1] +1 == 8 (NOT COORECT, to represent the 127 we need 7 bits only)

UGC NET November 2017 cs question paper solution set II Q18

Question 18

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Match the following with respect to RDBMS:

(a) Entity integrity	(i) enforces some specific business rule that do not fall  into entity or domain
(b) Domain integrity	(ii) Rows can’t be deleted which are used by other records
(c) Referential integrity	(iii) enforces valid entries for a column
(d) Userdefined integrity	(iv) No duplicate rows in a table

Code :

	(a)	(b)	(c)	(d)
(1)	(iii)	(iv)	(i)	(ii)
(2)	(iv)	(iii)	(ii)	(i)
(3)	(iv)	(ii)	(iii)	(i)
(4)	(ii)	(iii)	(iv)	(i)

Answer: 2

Explanation:

Entity integrity is defined by using primary key of table. it defines that table should not allow duplicate rows in table. Each row in the Table is identified by unique and non-null key called primary key.
Here option (a) match with (iv)  > ( a - iv )

Domain integrity specifies that all columns in a relational database must be declared based on a defined domain (Here domain means type of the column, it can be Integer, Varchar, Long, . etc).
If some table column has data type of integer then it will not allow any string values. That means this column value includes only Integer domain values.
Here option (b) match with (iii)  > ( b - iii )

Referential integrity implies that rows can't be deleted in master table if that are in use or referred by some other table.
Here option (c) match with (ii)  > (c-ii)

So, Correct answer should be option 2.

UGC NET November 2017, Q-9, Paper 2

Negation of the proposition ∃ x H(x) is :
(1) ∃x ¬ H(x)
(2) ∀ x ¬ H(x)
(3) ∀ x H(x)
(4) ¬ x H(x)

Ans is  (2) ∀ x ¬ H(x)

negation of (∃ x H(x)) =   ¬ ∃ x H(x)  =  ∀ x ¬ H(x)  (as negation symbol moves from left to right it changes the symbol  ∃ to ∀).

ISRO-previous-paper-2015 Computer Science question 18, Set A

Given a block can hold either 3 records or 10 key pointers. A database contains n records, then how many blocks do we need to hold the data file and the dense index

(a) 13n /30
(b) n/3
(c) n/10
(d) n/30

number of blocks to store the n pointers (as it's dense index, there exist a pointer(index record) for every search key ) is : n/10
number of blocks needed to store the n records : n/3


so answer is n/10 + n/3 = 13n/10

Refer below link to get more idea about the dense and sparse indexing.
https://stackoverflow.com/questions/36808877/difference-between-sparse-index-and-dense-index

ISRO-previous-paper-2017-Dec Computer Science question 3,Set A

❔ A bag contains 19 red balls and 19 black balls. Two balls are removed at a time repeatedly and discarded if they are of the same colour, but if they are different, black ball is discarded and red ball is returned to the bag. The probability that this process will terminate with one red ball is

a) 1
b) 1/21
c) 0
d) 0.5

Answer is 1:

there are 4 possible combinations of balls:

RR -- discard
RB -- keep red discard black
BR -- keep red discard black
BB -- discard

repeated combination comes for each above (RR,RB,BR,BB) then,
due odd number of balls:
the last combination in the bag is RB.

ISRO Scientist/Engineer 2017 Dec, Question 6, set A

❔ The proposition (P->Q)^(Q->P) is a

a) tautology
b) contradiction
c) contingency
d) absurdity

Answer is Contingency

as (P->Q)^(Q->P) equivalent to P⇔Q
These type of proposition are neither a tautology nor a contradiction.

Below truth table shows that the proposition holds true for two cases : so its contingency
here, 1 means true and 0 means false

P	Q	P⇔Q
0	0	1
0	1	0
1	0	0
1	1	1

ISRO previous paper 2013, Computer Science question 49, set A

What is the least value of the function f(x) = 2x²-8x-3 in the interval [0,5] ?
(a) -15
(b) -7
(c) -11
(d) -3

Answer is (a),

f '(x) = 2x-8

Let  f '(x) = 4x-8=0,
then, x=2,
substitute x=2 to the f ", but here no need to substitue in f ".

f ''(x) = 4 >0 (positive >> Minimum occurs at this point),

Refer this:
above question similar to Example 3  in below link:

https://www.math.wvu.edu/~hjlai/Words2Algebra/MinMax_Closed_Interva.pdf

ISRO previous paper 2017 December, Computer Science question 13, set A

❔ Consider the following schema :

Sailors(sid,sname,rating,age)
Boats(bid,bname, colour)
Reserves(sid,bid,day)

Two boats can have the same name but the colour differentiates them.
The two relations

 ρ(Tempsids, (π_{sid, bid} Reserves) / (π_bid ( σ _{bname='Ganga'} Boats))),
π_sname(Tempsids ⋈ Sailors)

If / is division operation, the above set of relations represents the query
(a) Names of sailors who have reserved all boats called Ganga
(b) Names of sailors who have not reserved any Ganga boat
(c) Names of sailors who have reserved at least one Ganga boat
(d) Names of sailors who have reserved at most one Ganga boat

Answer is (a),

best refer to you tube video to understand the concept of division operation in DBMS.

Division Operator in DBMS Relational Algebra with Example in English, Hindi