Number of Subsets of a given Set:

If a set contains ‘n’ elements, then the number of subsets of the set is 2\(^{n}\).

Number of Proper Subsets of the Set:

If a set contains ‘n’ elements, then the number of proper subsets of the set is 2\(^{n}\) - 1.

If A = {p, q} the proper subsets of A are [{ }, {p}, {q}]

⇒ Number of proper subsets of A are 3 = 2\(^{2}\) - 1 = 4 - 1

In general, number of proper subsets of a given set = 2\(^{m}\) - 1, where m is the number of elements.

**For
example: **

**1.** If A {1, 3, 5}, then write all the
possible subsets of A. Find their numbers.

**Solution: **

The subset of A containing no elements - { }

The subset of A containing one element each - {1} {3} {5}

The subset of A containing two elements each - {1, 3} {1, 5} {3, 5}

The subset of A containing three elements - {1, 3, 5)

Therefore, all possible subsets of A are { }, {1}, {3}, {5}, {1, 3}, {1, 5}, {3, 5}, {1, 3, 5}

Therefore, number of all possible subsets of A is 8 which is equal 2\(^{3}\).

Proper subsets are = { }, {1}, {3}, {5}, {1, 3}, {1, 5}, {3, 5}

Number of proper subsets are 7 = 8 - 1 = 2\(^{3}\) - 1

**2.** If the number of elements in a set is 2,
find the number of subsets and proper subsets.

Solution:

Number of elements in a set = 2

Then, number of subsets = 2\(^{2}\) = 4

Also, the number of proper subsets = 2\(^{2}\) - 1

= 4 – 1 = 3

**3.** If A = {1, 2, 3, 4, 5}

then the number of proper subsets = 2\(^{5}\) - 1

= 32 - 1 = 31 {Take [2\(^{n}\) - 1]}

and
power set of A = 2\(^{5}\) = 32 {Take [2\(^{n}\)]}

● **Set Theory**

●** Sets**

**● **Subset

**7th Grade Math Problems**

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