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# Class 11-science NCERT Solutions Maths Chapter 1 - Sets

## Sets Exercise Ex. 1.1

### Solution 1

Hence: this collection is a set.

(vii) The collection of all even integers is a well-defined collection because one can definitely identify an even integer that belongs to this collection.

Hence: this collection is a set.

(viii) The collection of questions in this chapter is a well-defined collection because one can definitely identify a question that belongs to this chapter.

Hence: this collection is a set.

(ix) The collection ofmost dangerous animals of the world is not a well-defined collection because the criteria for determining the dangerousness of an animal can vary from person to person.

Hence: this collection is not a set.

### Solution 3

(i) A = { x : x is an integer and -3 ≤ x < 7}.

The elements of this set are -3, -2, -1, 0, 1, 2, 3, 4, 5 and 6 only.

Therefore, the given set can written in roster form as

A = {-3, -2, -1, 0, 1, 2, 3, 4, 5, 6}

(ii) B = { x : x is a natural number less than 6}

The elements of this set are 1, 2, 3, 4 and 5 only.

Therefore, the given set can written in roster form as

B = {1, 2, 3, 4, 5}

(iii) C = { x : x is a two-digit number such that the sum of its digits is 8}

The elements of this set are 17, 26, 35, 44, 53, 62, 71 and 80 only.

Therefore, the given set can written in roster form as

C = {17, 26, 35, 44, 53, 62, 71, 80}

(iv) D = { x : x is a prime number which is divisor of 60}.

 2 60 2 30 3 15 5

∴ 60 = 2 × 2 × 3 × 5

The elements of this set are 2, 3 and 5 only.

Therefore, this set can written in roster form as D = {2, 3, 5}.

(v) E = The set of all letters in the word TRIGONOMETRY.

There are 12 letters in the word TRIGONOMETRY, out of which letters T, R, and O are repeated.

Therefore, this set can written in roster form as

E = {T, R, I, G, O, N, M, E, Y}

(vi) F = The set of all letters in the word BETTER.

There are 6 letters in the word BETTER, out of which letters E and T are repeated.

Therefore, this set can written in roster form as

F = {B, E, T, R}