NCERT Solutions for Class 11 Maths Chapter 1 Sets Ex 1.1
Ex 1.1 Class 11 Maths Question 1.
Which of the following are sets? Justify your answer.(i) The collection of all the months of a year beginning with the letter J.
(ii) The collection of ten most talented writers of India.
(iii) A team of eleven best-cricket batsmen of the world.
(iv) The collection of all boys in your class.
(v) The collection of all natural numbers less than 100.
(vi) A collection of novels written by the writer Munshi Prem Chand.
(vii) The collection of all even integers.
(viii) The collection of questions in this chapter.
(ix) A collection of most dangerous animals of world.
Solution.
(i) The collection of all months of a year beginning with J is
{January, June, July}, which is well-defined and hence it is a set.
(ii) The collection of most talented writers of India is not well-defined
because opinions about ‘most talented writers’ may vary from person to person
and hence it is not a set.
(iii) A team of eleven best-cricket batsmen of the world is not
well-defined because opinions about ‘best-cricket batsmen’ may vary from person
to person and hence it is not a set.
(iv) The collection of all boys in your class is well-defined and
hence it is a set.
(v) The collection of all natural numbers less than 100 is {1, 2,
3, 4, …………, 99}, which is well-defined and hence it is a set.
(vi) A collection of novels written by the writer Munshi Prem Chand
is well-defined and hence it is a set.
(vii) The collection of all even integers is {…………..,-4, -2, 0, 2,
4,……….. } which is well-defined and hence it is a set.
(viii) The collection of questions in this chapter is well-defined
and hence it is a set.
(ix) A collection of most dangerous animals of the world is not
well-defined because opinions about ‘most dangerous animals’ may vary from
person to person and hence it is not a set.
Ex 1.1 Class 11 Maths Question 2.
Let A = {1, 2, 3, 4, 5, 6). Insert the appropriate symbol ∈ or ∉ in the blank spaces:(i) 5…A
(ii) 8…A
(iii) 0…A
(iv) 4…A
(v) 2…A
(vi) 10…A
Solution.
(i) Since 5 is the element
of set A. ∴ 5 ∈ A.
(ii) Since
8 is not the element of set A. ∴ 8 ∉ A
(iii) Since
0 is not the element of set A ∴ 0 ∉ A.
(iv) Since
4 is the element of set A. ∴ 4 ∈ A.
(v) Since
2 is the element of set A. ∴ 2 ∈ A.
(vi) Since
10 is not the element of set A. ∴ 10 ∉ A.
Ex 1.1 Class 11 Maths Question 3.
Write the following sets in roster form:(i) A = {x: x is an integer and -3 < x < 7}
(ii) B = {x: x is a natural number less than 6}
(iii) C = {x: x is a two-digit natural number such that the sum of its digits is 8}
(v) E = The set of all letters in the word TRIGONOMETRY
(vi) F = The set of all letters in the word BETTER
Solution.
(i) A
= {x: x is an integer and -3 < x < 7}
Since integers lying between -3 and 7 are
-2, -1, 0, 1, 2, 3, 4, 5, 6.
∴ A = {-2, -1, 0, 1, 2, 3, 4, 5, 6}.
(ii) B = {x: x is a natural number less
than 6}
Since natural numbers less than 6 are 1, 2, 3, 4, 5.
∴ B = {1, 2, 3, 4, 5}
(iii) C = {x: x is a two-digit natural
number such that the sum of its digits is 8}
Since two-digit natural numbers such that the sum of its digits is 8 are 17,
26, 35, 44, 53, 62, 71, 80.
∴ C = {17, 26, 35, 44, 53, 62, 71, 80}
(iv) D = {x: x is a prime number which is divisor of 60}
Since prime numbers which are divisors of 60 are 2, 3, 5.
∴ D = {2, 3, 5}
(v) F = The set of all letters in the
word TRIGONOMETRY
Since the letters in the word
TRIGONOMETRY are T, R, I, G, O, N, M, E, Y.
∴ E = (T, R, I, G, O, N, M, E, Y}
(vi) F = The set of all letters in the
word BETTER
The word BETTER is formed by
using the letters B, E, T, R.
∴ F = (B, E, T, R}
Ex 1.1 Class 11 Maths Question 4.
Write the following sets in the set-builder form:(i) {3, 6, 9, 12}
(ii) {2, 4, 8, 16, 32}
(iii) {5, 25, 125, 625}
(iv) {2, 4, 6, …}
(v) {1, 4, 9, …….., 100}
Solution.
(i) Let
A = (3, 6, 9, 12}
All elements of the set are natural numbers that are multiples of 3.
∴ A = (x: x = 3n, n ∈ N and 1 ≤ n ≤ 4}
(ii) Let B = (2, 4, 8, 16, 32} = (21,
22, 23, 24, 25}
∴ B = {x: x = 2n, n ∈ N and 1 ≤ n ≤ 5}
(iii) Let C = (5, 25, 125, 625} = (51,
52, 53, 54}
∴ C = {x: x = 5n, n ∈ N and 1 ≤ n ≤ 4}
(iv) Let D = (2, 4, 6, …}
All elements of the set are even natural numbers.
∴ D = (x: x is an even natural number}
(v) Let E = {1, 4, 9, ………., 100}
All elements of the set are perfect squares.
∴ E = {x: x = n2, n ∈ N and 1 ≤ n ≤ 10}
Ex 1.1 Class 11 Maths Question 5.
List all the elements of the following sets:(i) A = {x: x is an odd natural number}
(ii) B = {x: x is an integer, −1/2 < x < 9/2}
(iii) C = {x: x is an integer, x2 ≤ 4}
(iv) D = {x: x is a letter in the word “LOYAL”}
(v) E = {x: x is a month of a year not having 31 days}
(vi) F = {x : x is a consonant in the English alphabet which precedes k}
Solution.
(i) A
= {x: x is an odd natural number}
∴ A = {1, 3, 5, 7, ………}
(ii) B = {x: x is an integer, −1/2 < x
< 9/2}
∴ B = {0, 1, 2, 3, 4}
(iii) C = {x: x is an integer, x2 ≤
4}
x2 ≤ 4 ⇒ -2 ≤ x ≤ 2
∴ C = {-2, -1, 0, 1, 2}
(iv) D = {x: x is a letter in the word
“LOYAL”}
∴ D = {L, O, Y, A}
(v) E = {x: x is a month of a year not
having 31 days}
∴ E = {February, April, June, September,
November}
(vi) F = {x: x is a consonant in the
English alphabet which precedes k}
∴ F = {b, c, d, f, g, h, j}
Ex 1.1 Class 11 Maths Question 6.
Match each of the set on the left in the roster form with the same set on the right described in set-builder form:i. {1, 2, 3, 6} (a) {x: x is a prime number and a divisor of 6}
ii. {2, 3} (b) {x: x is an odd natural number less than 10}
iii. {M, A, T, H, E, I, C, S} (c) {x: x is natural number and divisor of 6} iv. {1, 3, 5, 7, 9} (d) {x: x is a letter of the word MATHEMATICS}
Solution.
(i) →
(c),
(ii) →
(a),
(iii) →
(d),
(iv) →
(b).
Related Links:
NCERT Solutions for Maths Class 9