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In this Class 10 Mathematics topic from the chapter “Sets,” students learn how to describe and represent a collection of well-defined objects using clear mathematical language. They explore common forms such as descriptive statements, roster or tabular notation, and set-builder notation, while identifying elements and understanding the symbols used for membership and non-membership. The topic builds accuracy in reading, writing, comparing, and interpreting sets, providing a foundation for later ideas involving relationships and operations on sets.
TOPIC PRACTICE
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Hard · Level 1View options
K = {4, 9, 25}
K = {4, 8, 9, 16, 25, 27}
K = {2, 3, 5, 7}
K = {1, 4, 9, 16, 25, 36}
Hard · Level 1View options
A = {-4, -3, -2, -1, 0, 1, 4}
A = {-4, -3, -2, -1, 0, 1, 2, 3, 4}
A = {-4, -1, 0, 1, 4}
A = {0, 1, 4}
Hard · Level 1View options
10
8
11
12
Hard · Level 1View options
40
37
70
86
Question 1HardLevel 1
If K = {x : x ∈ N, x < 40 and x has exactly three positive divisors}, what is K?
Correct answer: A
A positive integer has exactly three positive divisors precisely when it is the square of a prime: if x = p², its divisors are 1, p, and p². The prime squares less than 40 are 2² = 4, 3² = 9, and 5² = 25. The next prime square, 7² = 49, is not less than 40. Hence K = {4, 9, 25}.
Which is the roster form of A = {x ∈ Z : x² ≤ 16 and x is not prime}?
Correct answer: A
The inequality x² ≤ 16 gives -4 ≤ x ≤ 4, so the integer candidates are -4, -3, -2, -1, 0, 1, 2, 3, and 4. Among these, the only prime numbers are 2 and 3. Removing them leaves -4, -3, -2, -1, 0, 1, and 4. Negative integers, zero, and one are not prime by the definition of a prime number.
How many elements are there in M = {x ∈ N : x < 40 and x is divisible by 6 or 9}?
Correct answer: B
The positive multiples of 6 below 40 are 6, 12, 18, 24, 30, and 36. The positive multiples of 9 below 40 are 9, 18, 27, and 36. Taking the union gives {6, 9, 12, 18, 24, 27, 30, 36}, which has 8 elements. The common multiples 18 and 36 are counted only once because a set has no repeated elements.
If n(U) = 110, n(A) = 58, n(B) = 49 and n(A − B) = 21, then what is n((A ∪ B)′)?
Correct answer: A
The set A consists of the part only in A and the common part. Therefore, n(A ∩ B) = n(A) − n(A − B) = 58 − 21 = 37. Then n(A ∪ B) = 58 + 49 − 37 = 70. The complement contains the elements of U outside this union, so n((A ∪ B)′) = 110 − 70 = 40. Option A is correct.
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