 Sample Questions, Previous Year Solved Papers, Study Materials For Competitive Examinations Like UGC NET, SET And GATE Computer Science.

Thursday, 26 January 2017

21.       Given the following statements :
(A) A class of languages that is closed under union and complementation has to be closed under intersection.
(B) A class of languages that is closed under union and intersection has to be closed under complementation.
Which of the following options is correct?
(1) Both (A) and (B) are false.
(2) Both (A) and (B) are true.
(3) (A) is true, (B) is false.
(4) (A) is false, (B) is true.
22.       Let G = (V,T,S,P) be a context-free grammar such that every one of its productions is of the form A→v, with |v| = K>1. The derivation tree for any W ϵ L(G) has a height h such that
23.       Given the following two languages:
L1 = {anbn|n≥0, n≠100}
L2 = {w ϵ {a,b,c}*| na(w) = nb(w) = nc(w)}
Which of the following options is correct?
(1) Both L1 and L2 are not context free language.
(2) Both L1 and L2 are context free language.
(3) L1 is context free language, L2 is not context free language.
(4) L1 is not context free language, L2 is context free language.
24.       A recursive function h, is defined as follows:
h(m)=k, if m=0
= 1, if m=1
= 2h(m-1) + 4h(m-2), if m≥2
If the value of h(4) is 88 then the value of k is:
(1) 0
(2) 1
(3) 2
(4) -1
25.       Suppose there are n stations in a slotted LAN. Each station attempts to transmit with a probability P in each time slot. The probability that only one station transmits in a given slot is ..................
(1) nP(1-P)n-1
(2) nP
(3) P(1-P)n-1
(4) nP(1-P)n-1

26.       Station A uses 32 byte packets to transmit messages to station B using sliding window protocol. The round trip delay between A and B is 40 milli seconds and the bottleneck bandwidth on the path between A and B is 64 kbps. The optimal window size of A is
(1) 20
(2) 10
(3) 30
(4) 40
27.       Let G(x) be generator polynomial used for CRC checking. The condition that should be satisfied by G(x) to correct odd numbered error bits, will be:
(1) (1+x) is factor of G(x)
(2) (1-x) is factor of G(x)
(3) (1+x2) is factor of G(x)
(4) x is factor of G(x)
28.       In a packet switching network, if the message size is 48 bytes and each packet contains a header of 3 bytes. If 24 packets are required to transmit the message, the packet size is ................
(1) 2 bytes
(2) 1 byte
(3) 4 bytes
(4) 5 bytes
29.       In RSA public key cryptosystem suppose n=p*q where p and q are primes. (e,n) and (d,n) are public and private keys respectively. Let M be an integer such that 0<M<n and ɸ(n)=(p-1)(q-1).
Which of the following equations represent RSA public key cryptosystem?
I. C≡Me (mod n), M≡(C)d(mod n)
II. ed≡1(mod n)
III. ed≡(mod ɸ(n))
IV. C≡Me (mod ɸn), M≡Cd(mod ɸn)
Codes:
(1) I and II
(2) I and III
(3) II and III
(4) I and IV