Answers: (i) We know that, A ∪ (A ∩ B) [A ∪ A = A] (A ∪ A) ∩ (A ∪ B) ∴ A ∩ (A ∪ B) = A (ii) A ∩ (A ∪ B) = A We know that, (A ∩ A) ∪ (A ∩ B) [A ∩ A = A] ∴ A ∪ (A ∩ B) =...
For three sets A, B, and C, show that (i) A ∩ B = A ∩ C need not imply B = C. (ii) A ⊂ B ⇒ C – B ⊂ C – A
Answers: (i) Consider, A = {1, 2} B = {2, 3} C = {2, 4} A ∩ B = {2} A ∩ C = {2} Thus, A ∩ B = A ∩ C and B is not equal to C. (ii) A ⊂ B C–B ⊂ C–A Consider, x ∈ C– B x ∈ C and x ∉ B x ∈ C and x ∉ A...
For any two sets A and B, show that the following statements are equivalent: (i) A ∪ B = B (ii) A ∩ B = A
Answers: (i) A ∪ B = B Proving, (iii)=(iv) Let us take, A ∪ B = B A ∩ B = A. A ⊂ B and A ∩ B = A Thus, (iii)=(iv) is proved. (ii) A ∩ B = A Proving, (iv)=(i) Let us take, A ∩ B = A A ⊂ B A ∩ B = A...
For any two sets A and B, show that the following statements are equivalent: (i) A ⊂ B (ii) A – B = ϕ
Answers: (i) A ⊂ B Proving, (i)=(ii) ( A ⊂ B) A–B = {x ∈ A: x ∉ B} All element of A is also an element of B ∴ A–B = ϕ Thus, (i)=(ii) Proved. (ii) A – B = ϕ Proving, (ii)=(iii) Let us take, A–B = ϕ...
For any two sets A and B, prove that A ⊂ B ⇒ A ∩ B = A
Answer: A ⊂ B ⇒ A ∩ B = A Consider, p ∈ A ⊂ B x ∈ B Let, p ∈ A ∩ B x ∈ A and x ∈ B x ∈ A and x ∈ A ∴ (A ∩ B) = A
For any two sets A and B, prove that (i) B ⊂ A ∪ B (ii) A ∩ B ⊂ A
Answers: (i) Consider, p ∈ B p ∈ B ∪ A ∴ B ⊂ A ∪ B (ii) Consider, p ∈ A ∩ B p ∈ A and p ∈ B ∴ A ∩ B ⊂ A
If U = {2, 3, 5, 7, 9} is the universal set and A = {3, 7}, B = {2, 5, 7, 9}, then prove that: (i) (A ∪ B)’ = A’ ∩ B’ (ii) (A ∩ B)’ = A’ ∪ B’
Answers: (i) LHS, A ∪ B = {x: x ∈ A or x ∈ B} A ∪ B = {2, 3, 5, 7, 9} (A∪B)’ = Complement of (A∪B) with U. (A∪B)’ = U – (A∪B)’ U – (A∪B)’ = {x ∈ U: x ∉ (A∪B)’} U = {2, 3, 5, 7, 9} (A∪B)’ = {2, 3,...
Let A = {1, 2, 4, 5} B = {2, 3, 5, 6} C = {4, 5, 6, 7}. Verify the following identities: (i) A – (B ∩ C) = (A – B) ∪ (A – C) (ii) A ∩ (B △ C) = (A ∩ B) △ (A ∩ C)
Answers: (i) LHS, (B ∩ C) = {x: x ∈ B and x ∈ C} (B ∩ C) = {5, 6} A – (B ∩ C) = {x ∈ A: x ∉ (B ∩ C)} A = {1, 2, 4, 5} (B ∩ C) = {5, 6} (A – (B ∩ C)) = {1, 2, 4} RHS, A – B = {x ∈ A: x ∉ B} A = {1,...
Let A = {1, 2, 4, 5} B = {2, 3, 5, 6} C = {4, 5, 6, 7}. Verify the following identities: (i) A ∩ (B – C) = (A ∩ B) – (A ∩ C) (ii) A – (B ∪ C) = (A – B) ∩ (A – C)
Answers: (i) LHS, B–C = {x ∈ B: x ∉ C} B = {2, 3, 5, 6} C = {4, 5, 6, 7} B–C = {2, 3} (A ∩ (B – C)) = {x: x ∈ A and x ∈ (B – C)} (A ∩ (B – C)) = {2} RHS, (A ∩ B) = {x: x ∈ A and x ∈ B} (A ∩ B) =...
Let A = {1, 2, 4, 5} B = {2, 3, 5, 6} C = {4, 5, 6, 7}. Verify the following identities: (i) A ∪ (B ∩ C) = (A ∪ B) ∩ (A ∪ C) (ii) A ∩ (B ∪ C) = (A ∩ B) ∪ (A ∩ C)
Answers: (i) LHS, (B ∩ C) = {x: x ∈ B and x ∈ C} (B ∩ C) = {5, 6} A ∪ (B ∩ C) = {x: x ∈ A or x ∈ (B ∩ C)} A ∪ (B ∩ C) = {1, 2, 4, 5, 6} RHS, (A ∪ B) = {x: x ∈ A or x ∈ B} (A ∪ B) = {1, 2, 4, 5, 6}....
Find the smallest set A such that A ∪ {1, 2} = {1, 2, 3, 5, 9}.
Answer: A ∪ {1, 2} = {1, 2, 3, 5, 9} The smallest set of A, A = {1, 2, 3, 5, 9} – {1, 2} ∴ A = {3, 5, 9}
In a committee, 50 people speak French, 20 speak Spanish and 10 speak both Spanish and French. How many speak at least one of these two languages?
Solution: Let’s consider as the set of people in the committee who speak French as F, and the set of people in the committee who speak Spanish as S. $n\left( F \right)\text{ }=\text{ }50$ $n\left( S...
In a group of 65 people, 40 like cricket, 10 like both cricket and tennis. How many like tennis only and not cricket? How many like tennis?
Solution: Let’s consider C as the set of people who like cricket, and the set of people who like tennis as T. $n(C~\cup ~T)\text{ }=\text{ }65$ $n\left( C \right)\text{ }=\text{ }40$ $n(C~\cap...
In a group of 70 people, 37 like coffee, 52 like tea, and each person likes at least one of the two drinks. How many people like both coffee and tea?
Solution: Let’s consider the set of people who like coffee as C, and the set of people who like tea as T. $n(C~\cup ~T)\text{ }=\text{ }70$ $n\left( C \right)\text{ }=\text{ }37$ $n\left( T...
If X and Y are two sets such that X has 40 elements, X ∪Y has 60 elements and X ∩Y has 10 elements, how many elements does Y have?
Solution: It is known that $n\left( X \right)\text{ }=\text{ }40$ $n(X~\cup ~Y)\text{ }=\text{ }60$ $n(X~\cap ~Y)\text{ }=\text{ }10$ This can be written as $n(X~\cup ~Y)\text{ }=~n\left( X...
If S and T are two sets such that S has 21 elements, T has 32 elements, and S ∩ T has 11 elements, how many elements does S ∪ T have?
Solution: It is known that $n\left( S \right)\text{ }=\text{ }21$ $n\left( T \right)\text{ }=\text{ }32$ $n(S~\cap ~T)\text{ }=\text{ }11$ This can be written as $n~(S~\cup ~T)\text{ }=~n~\left( S...
In a group of 400 people, 250 can speak Hindi and 200 can speak English. How many people can speak both Hindi and English?
Solution: Let’s consider the set of people who speak Hindi as H, and the set of people who speak English as E. It is known that $n(H~\cup ~E)\text{ }=\text{ }400$ $n\left( H \right)\text{ }=\text{...
If X and Y are two sets such that X ∪ Y has 18 elements, X has 8 elements and Y has 15 elements; how many elements does X ∩ Y have?
Solution: Provided $n\text{ }\left( X\text{ }\cup \text{ }Y \right)\text{ }=\text{ }18$ $n\text{ }\left( X \right)\text{ }=\text{ }8$ $n\text{ }\left( Y \right)\text{ }=\text{ }15$ This can be...
If X and Y are two sets such that n(X) = 17, n(Y) = 23 and n(X ∪ Y) = 38, find n(X ∩ Y).
Solution: Provided $n\text{ }\left( X \right)\text{ }=\text{ }17$ $n\text{ }\left( Y \right)\text{ }=\text{ }23$ $n\text{ }\left( X\text{ }\cup \text{ }Y \right)\text{ }=\text{ }38$ This can be...