Question:

In a survey of $60$ people, it was found that $25$ people read newspaper $H$, $26$ read newspaper $T$, $26$ read newspaper $I$, $9$ read both $H$ and $I$, $11$ read both $H$ and $T$, $8$ read both $T$ and $I$, $3$ read all three newspapers. Which of the following statements is/are true? : The number of people who read exactly one newspaper is $30$. : Exactly one of the newspaper read is $n(H) + n(T) + n(I) - 2\{n(H \cap I) + n(H \cap T) + n(T \cap T)\}$ $+ 3n(H \cap T \cap I)$

Updated On: Jul 6, 2022
  • Only Statement-I
  • Only Statement-II
  • Both Statement-I and Statement-II
  • Neither Statement-I nor Statement-II
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The Correct Option is C

Solution and Explanation

Given, $n(H) = 25$, $n(T) = 26$, $n(I) = 26$, $n(H \cap I) = 9$, $n(H \cap T) = 11$, $n (T \cap I) = 8$ and $n(H \cap T \cap I) = 3$ $\therefore$ Number of people who read exactly one newspaper $= n(H) + n(T) + n(I) - 2\{n(H \cap I) + n (H \cap I) + n(T \cap I)\}$ $+ 3n(H \cap T \cap I)$ $= 25 + 26 + 26 - 2(9 + 11 + 8) + 3 \times 3 = 30$
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Concepts Used:

Sets

Set is the collection of well defined objects. Sets are represented by capital letters, eg. A={}. Sets are composed of elements which could be numbers, letters, shapes, etc.

Example of set: Set of vowels A={a,e,i,o,u}

Representation of Sets

There are three basic notation or representation of sets are as follows:

Statement Form: The statement representation describes a statement to show what are the elements of a set.

  • For example, Set A is the list of the first five odd numbers.

Roster Form: The form in which elements are listed in set. Elements in the set is seperatrd by comma and enclosed within the curly braces.

  • For example represent the set of vowels in roster form.

A={a,e,i,o,u}

Set Builder Form: 

  1. The set builder representation has a certain rule or a statement that specifically describes the common feature of all the elements of a set.
  2. The set builder form uses a vertical bar in its representation, with a text describing the character of the elements of the set.
  3. For example, A = { k | k is an even number, k ≤ 20}. The statement says, all the elements of set A are even numbers that are less than or equal to 20.
  4. Sometimes a ":" is used in the place of the "|".