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Sets

4 Board Maths previous year questions on Sets — options free on every question; 1 include the answer & explanation free, the rest unlock with PYQ Pass.

Q1 FREE PREVIEW

A survey shows that 63% of the people in a city read newspaper A whereas 76% read newspaper B. If x% of the people read both the newspapers, then a possible value of can be:

a

37

b

55

c

29

d

65

✓ Correct answer: b)

55

Explanation

Let the total number of people in the city be \( 100 \).

Also, let \( A \) denotes the set of people who read

newspaper \( A \) and \( B \) denotes the set of people who

read newspaper \( B \).

\[ n(A)=63, n(B)=76 \]

Clearly, \( n(A \cup B) \) Clearly

\[ \begin{aligned} & \Rightarrow \quad n(A)+n(B)-n(A \cap B) \leq 100 \\ & \Rightarrow \quad 63+76-x \leq 100 \Rightarrow x \geq 39 \\ & \text { Also, } x \leq 63 \quad \therefore 39 \leq x \leq 63 \end{aligned} \]

Also, \( x \leq 63 \quad \therefore 39 \leq x \leq 63 \)

So, the possible value of \( x \) can be \( 55 \).

Q2

If \(A=\{x \in R:|x|<2\}\) and \(B=\{x \in R:|x-2| \geq 3\}\), then:

a

\(B-A=R-(-2,5)\)

b

\(A \cap B=(-2,-1)\)

c

\(A-B=[-1,2)\)

d

\(A \cup B=R-(2,5)\)

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Q3

A set A has 3 elements and another set B has 6 elements. Then

a

\( 3 \leq n(A \cup B) \leq 6 \)

b

\(3 \leq n(A \cup B) \leq 9\)

c

\(6 \leq n(A \cup B) \leq 9\)

d

\(0 \leq n(A \cup B) \leq 9\)

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Q4

Consider the two sets: \(A=\left{m\in R\right.\) : both the roots of \({x}^{2}-(m+1)\)\(x=m+4\) are real} and \(B=[-3,5).\) Which of the following is not true?

a

\(\mathrm{A}\cap \mathrm{B}={-3}\)

b

\(B-A=(-3,5)\)

c

\(\mathrm{A}\cup \mathrm{B}=\mathrm{R}\)

d

\(\mathrm{A}-\mathrm{B}=(-\infty ,-3)\cup (5,\infty )\)

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