UGC NET PAPER 2 June 2019 Question 78 (Shift-I)

Question 78

---

78. Consider the following grammar:
S→ XY
X→ YaY | a and Y → bbX
Which of the following statements is/are true about the above grammar?
(a) Strings produced by the grammar can have consecutive three a's
(b) Every string produced by the grammar have alternate a and b
(c) Every string produced by the grammar have at least two a's
(d) Every string produced by the grammar have b's in multiple of 2.

1. 1. (a) only
2. 2. (b) and (c) only
3. 3. (d) only
4. 4. (c) and (d) only

Answer : 4. (c) and (d) only

Explanation Question 78

Given grammar generates strings which contains "b" in multiple of 2 and number of "a" at least 2.

This grammar generate a string set of this form, L = { abba, bbaabbabba, abbbbaabba, . . . . . . . . . . . . . }

• Statement (a) is not true because the grammar can generate two consecutive a’s but not three consecutive a’s.
• Statement (b) is not true because every string produced by the grammar do not have alternate a and b. The grammar can generate two b’s together it means that every string do not have alternate "a" and "b".
• Statement (c) is true because every string produced by the grammar have at least two a's.
• Statement (d) is true because every string produced by the grammar have b's in multiple of 2.

This is satisfied by statements c and d. But statements a and b are not satisfied.
Hence statements c and d is right.

So, option 4 is correct answer

Previous	Next
UGC NET CS 2018 July - II Question 77	UGC NET CS 2018 July - II Question 79