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 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