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Cardinality of a Set

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Topics

  • Definition: Cardinality
  • Examples
  • Real-Life Application
  • Key Points Summary
CISCE: Class 6

Definition: Cardinality

Cardinality refers to the number of distinct elements in a set.
It is denoted by n(A)

  • The cardinal number of the empty set is 0.
  • The cardinal number of an infinite set is not defined

CISCE: Class 6

Examples

1. Set P = {2, 9, 11, 14}

  • Has 4 elements,
  • So its cardinal number is n(P) = 4.

2. Set E = {} (empty set)

  • has 0 elements, 
  • n(E) = 0.

3. A = {2, 3, 5, 5, 3}

  • Set A has 3 unique elements: {2, 3, 5}
  • n(A) = 3

4. B = {letters in the word 'NOORAJAHAN'}

  • Set B has 6 unique letters: {n, o, r, a, j, h}
  • n(B) = 6

5. P = {counting numbers between 10 and 30 divisible by 5}

  • Set P contains {15, 20, 25}
  • n(P) = 3
CISCE: Class 6

Real-Life Application

Imagine you collect marbles of different colours:
Even if you have five red marbles and three blue ones, you only count red and blue as unique colours.
So, your set has two unique elements: n(Set) = 2

CISCE: Class 6

Key Points Summary

  • Cardinality counts only different items in a set.
  • Repeated items count once.
  • An empty set’s cardinality is zero.

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