Tag: complement of sets

Questions Related to complement of sets

If $U = \left {x|x\epsilon N, x < 5\right }, A = \left {x|x\epsilon N, x\leq 2\right }$ then $A' =$ __________.

  1. $\left {1, 2\right }$

  2. $\left {1, 2, 3, 4, 5\right }$

  3. $\left {3, 4\right }$

  4. $\left {3, 4, 5\right }$


Correct Option: C
Explanation:

$ \cup  = { x|x \in N,x < 5} $

${\rm A} = \left| {x|x \in N,x \leqslant 2} \right|$
then $A' = { 3,4} $
part $C$ is correct answer.

Comment true or false  on the following statements
$ A\cap \left( B-C \right) =\left( A\cap B \right) -\left( A\cap C \right)$

  1. True

  2. False


Correct Option: A
Explanation:

Let $x\in A\cap (B - C)$

$\Rightarrow x\in A$ and $x\in (B-C)$
$\Rightarrow x\in A$ and $(x\in B \text{ and } x \notin C)$
$\Rightarrow( x\in A \text{ and } x\in B)$ and $(x\in A \text{ and } x \notin C)$
$\Rightarrow (A\cap B) - (A\cap C)$
Hence true.

A survey on a sample of $25$ new cars being sold at a local auto dealer was conducted to see which of the three popular options - air-conditioning, radio and  power windows - were already installed.
The survey found:
$15$ had air-conditioning
$2$ had air-conditioning and power windows but no radios.
$12$ had power windows
$6$ had air-conditioning and radio but no power windows.
$11$ had radio.
$4$ had radio and power windows.
$3$ had all three options.
What is the number of cars that had none of the options?

  1. $4$

  2. $3$

  3. $1$

  4. $2$


Correct Option: D
Explanation:

$n(A\cup R\cup P)= n(A) +n(R) +n(P)-n(A\cap R)-n(R\cap P) -n(P\cap A) + n(A\cap R \cap P)$


$2= n(A\cap P)-n(A\cap P\cap R)$

$\Rightarrow n(A\cap P) = 2+3=5$

$6= n(A\cap R)-n(A\cap P\cap R)$

$\Rightarrow n(A\cap R) = 6+3=9$

$n(A\cup R\cup P)= n(A) +n(R) +n(P)-n(A\cap R)-n(R\cap P) -n(P\cap A) + n(A\cap R \cap P)$

$=15+11+12-9-5-4+3$

So answer $= 25-23 = 2$

With usual notations $n\left( A\cup B\cup C \right) =20,n\left( A\cap B\cap C\prime  \right) =2,n\left( B\cap C\cap A\prime  \right) =n\left( A\cap C\cap B\prime  \right) =4\quad$

$ and\quad n\left( A\cap B\cap C \right) =1$, then the number of elements belonging to exactly one of the sets is

  1. $9$

  2. $13$

  3. $14$

  4. $16$


Correct Option: A

Let $n(u)=700,n(A)=200,n(B)=300$
$n\left( A\cap B \right) =100,n\left( A^{\prime} \cap B^{\prime}  \right) =$

  1. $400$

  2. $600$

  3. $300$

  4. $None$


Correct Option: C
Explanation:

Ans. $(c). n(A\cap B)=n(A\cup B)$
$=n(u)-n(A\cup B)$
$=n(u)-\left{ n\left( A \right) +n\left( B \right) -n\left( A\cap B \right)  \right}$
$=700-\left{ 200+300-100 \right} = 300$

The value of $(A\cup B\cup C)\cap {(A\cap {B}^{c}\cap {C}^{c})}^{c}\cap {C}^{c}$

  1. $B\cap {C}^{c}$

  2. ${B}^{c}\cap {C}^{c}$

  3. $B\cap C$

  4. $A\cap B\cap C$


Correct Option: A

Given that the universal set,$ \xi =$ {x : 1 < x < 12 and x is an integer} and the sets P = {x : x is a prime number}, Q = {x : x is a multiple of 4} and R = {2, 3, 8, 9} the elements of the set $(Q \cup R)' \cap P$ are:

  1. {2, 3}

  2. {2, 3, 5}

  3. {5, 7, 11}

  4. {1, 5, 7, 11}


Correct Option: C
Explanation:

$Q={4,8};$     $P={2,3,5,7,11}$;     


$Q\cup R ={2.3.4.8.9}$

$(Q\cup R)' = {5,6,7,10,11}$

$(Q\cup R)'\cap P = {5,7,11}$

$(A'-B) \cup (B-A)=$

  1. $A$

  2. $A'$

  3. $B$

  4. $B'$


Correct Option: B
Explanation:

$(A'-B)\cup (B-A)$
$=A'\cap B'\cup B\cap A'$      $[\because A-B=A\cup B']$
$=A'\cap B'\cup A'\cap B$      $[\because A\cup B=B\cup A]$
$=A'\cap (B'\cup B)$
$=A'\cap U$
$=A'$
answer is B

if $X' = Y$ then $\displaystyle \left (X \cap Y  \right )'$ is equal to 

  1. $\displaystyle \phi $

  2. $X$

  3. $U$

  4. $Y$


Correct Option: C
Explanation:

Given 

$X' = Y$
$X$ $\cap$ $Y = X$ $\cap$  $X'$
$(X$ $\cup$ $X')' $ $= U $(Universal set)
Complement  of null set is Universal set $U$.