9th standard Guide,

# 9th Maths Solutions Chapter 1 Set Language Ex 1.1

## 9th Maths Solutions Chapter 1 Set Language Ex 1.1

1.Which of the following are sets?

(i) The collection of prime numbers upto 100

(ii) The collection of rich people in India

(iii) The collection of all rivers in India

(iv) The collection of good hockey players

Solution:

(i) It is a set

(ii) It is not a set (The word “rich” is not well defined)

(iii) It is a set

(iv) It is not a set (The word “good” is not well defined)

2.List the set of letters of the following words in Roster form.

(i) INDIA

(ii) PARALLELOGRAM

(iii) MISSISSIPPI

(iv) CZECHOSLOVAKIA

Solution:

(i) A = {I, N, D, A}

(ii) B = {P, A, R, L , E, O, G, M}

(iii) C = {M, I, S, P}

(iv) D = {C, Z, E, H, O, S, L, V, A, K, I}

3.Consider the following sets A = {0, 3, 5, 8}, B = {2, 4, 6, 10} and C = {12, 14, 18, 20}.

(a) State whether True or False:

(i) 18 ∈ C

(if) 6 ∉ A

(iii) 14 ∉ C

(iv) 10 ∈ B

(v) 5 ∈ B

(vi) 0 ∈ B

### (b) Fill in the blanks:

(i) 3 ∈ …………

(ii) 14 ∈…………

(iii) 18 ……….. B

(iv) 4 ………. B

4.Represent the following sets in Roster form.

(i) A = The set of all even natural numbers less than 20.

Answer : (i) A= {2, 4, 6, 8, 10, 12, 14, 16, 18}

(ii)B = {y : y = \frac{1}{2n}, n∈N, n ≤ 5}

Answer: (ii) B ={\frac{1}{2} , \frac{1}{4}, \frac{1}{6}, \frac{1}{8}, \frac{1}{10}}

(iii) C = {x : x is perfect cube, 27 < x < 216}

Answer : (iii) C = {64, 125}

(iv) D = {x : x ∈Z, – 5 < x ≤ 2}

Answer : (iv) D = {-4, -3, -2, -1, 0, 1, 2}

5.Represent the following sets in set builder form.

(i) B = The set of all cricket players in India who scored double centuries in one day internationals.

Answer :  (i) B = {x : x is a set of all cricket players in India who scored double centuries in one day internationals}

(ii) C = {12, 23, 34, …….}

Answer : (ii) C = {x : n ∈ N, x = nn+1 }

(iii) D = The set of all Tamil months in a year.

Answer : (iii) D = {x : x ∈ set of all Tamil months in a year}

(iv) E = The set of odd Whole numbers less than 9.

Answer : (iv) E = {x : x is an odd whole number and x < 9}

6.Represent the following sets in descriptive form.

(i) P = { January, June, July}

Answer : (i) P = The set of all months beginning with the letter “J”

(ii) Q = {7, 11, 13, 17, 19, 23, 29}

Answer : (ii) Q = The set of all prime numbers between 5 and 31

(iii) R = {x : x∈N, x < 5}

Answer : (iii) R = The set of natural numbers less than 5

(iv) S = {x : x is a consonant in English alphabets}

Answer : (iv) S = The set of consonants in English alphabets