Maharashtra State Board
Chapter 1: Sets
Practice Set 1.2 Solutions
Q.1 Decide which of the following are equal sets and which are not? Justify your answer.
A = { x | 3x – 1 = 2 }
Answer: A = {1}
(Because solving 3x – 1 = 2 ⇒ 3x = 3 ⇒ x = 1)
B = { x | x is a natural number but x is neither prime nor composite }
Answer: B = {1}
(Because the only natural number which is neither prime nor composite is 1)
C = { x | x ∈ N, x < 2 }
Answer: C = {1}
(Because 1 is the only natural number less than 2)
∴ Therefore, A = B = C. (All three sets are equal)
Q.2 Decide whether set A and B are equal sets. Give reason for your answer.
A = Even prime numbers
Answer: A = {2}
(Because 2 is the only even prime number)
B = { x | 7x – 1 = 13 }
Answer: B = {2}
(Because solving 7x – 1 = 13 ⇒ 7x = 14 ⇒ x = 2)
∴ Therefore, A = B. (Both sets are equal)
Q.3 Which of the following are empty sets? Why?
(i) A = { a | a is a natural number smaller than zero }
Answer: A = ∅ (empty)
(Because no natural number is smaller than zero)
(ii) B = { x | x² = 0 }
Answer: B = {0}
(Because x² = 0 ⇒ x = 0, so set contains 0 and is not empty)
(iii) C = { x | 5x – 2 = 0, x ∈ N }
Answer: C = ∅
(Because 5x – 2 = 0 ⇒ x = 2/5, which is not a natural number)
Q.4 Write with reasons, which of the following sets are finite or infinite.
(i) A = { x | x < 10, x is a natural number }
Answer: Finite
(Because A = {1,2,3,…,9} — only 9 elements)
(ii) B = { y | y < –1, y is an integer }
Answer: Infinite
(Because integers less than –1 continue without end)
(iii) C = Set of students of class 9 from your school
Answer: Finite
(Because number of students is limited)
(iv) Set of people from your village
Answer: Finite
(Because the village population is countable)
(v) Set of apparatus in laboratory
Answer: Finite
(Because laboratory apparatus are limited)
(vi) Set of whole numbers
Answer: Infinite
(Because whole numbers = {0,1,2,…} go on endlessly)
(vii) Set of rational numbers
Answer: Infinite
(Because rational numbers are endless)
Class 9 Maths Digest
- Practice Set 1.1 Class 9 Answers
- Practice Set 1.2 Class 9 Answers
- Practice Set 1.3 Class 9 Answers
- Practice Set 1.4 Class 9 Answers
- Problem Set 1 Class 9 Answers
- Practice Set 2.1 Class 9 Answers
- Practice Set 2.2 Class 9 Answers
- Practice Set 2.3 Class 9 Answers
- Practice Set 2.4 Class 9 Answers
- Practice Set 2.5 Class 9 Answers
- Problem Set 2 Class 9 Answers
