# Sets Formulas

Set formulas are the formulas associated with set theory in mathematics. Set is a collection of well-defined objects and it has distinct elements. Knowledge of sets helps us apply the set formulas, in the areas related to statistics, probability, geometry, and sequences. Venn diagrams are popularly used to visualize set formulas to arrive at their proof. Let's learn about set formulas with a few solved examples.

## What Are the Sets Formulas?

Here is a list of set formulas from the set theory, that can be used for ready reference. Recall the notations, symbols, definitions, and properties of sets before the formula here.

- If n(A) and n(B) denote the number of elements in two finite sets A and B respectively, then for any two overlapping sets A and B, n(A∪B) = n(A) + n(B) - n(A⋂B)
- If A and B are disjoint sets, n(A∪B) = n(A) + n(B)
- If A, B and C are 3 finite sets in U then, n(A∪B∪C)= n(A) +n(B) + n(C) - n(B⋂C) - n (A⋂ B)- n (A⋂C) + n(A⋂B⋂C)

### Sets Formulas on Properties of Sets

Commutativity:

- A⋂B = B⋂A
- A∪B = B∪A

Associativity:

- A⋂ (B⋂C) = (A⋂B)⋂C
- A∪ (B∪C) = (A∪B)∪C

Distributivity:A ⋂(B∪C) = (A ⋂B) ∪ (A⋂C)

Idempotent Law:

- A ⋂ A = A
- A ∪ A = A

Law of Ø and ∪:

- A⋂ Ø = Ø
- U ⋂ A = A
- A ∪ Ø = A
- U ∪ A = U

### Sets Formulas of Complement Sets

- Complement Law : A∪A' = U, A⋂A' = Ø and A' = U - A
- De Morgan's Laws: (A ∪B)' = A' ⋂B' and (A⋂B)' = A' ∪ B'
- Law of Double complementation: (A')' = A
- Laws of Empty set and Universal Set: Ø' = ∪ and ∪' = Ø

### Sets Formulas of Difference of Sets

- A - A = Ø
- B - A = B⋂ A'
- B - A = B - (A⋂B)
- (A - B) = A if A⋂B = Ø
- (A - B) ⋂ C = (A⋂ C) - (B⋂C)
- A ΔB = (A-B) U (B- A)
- n(AUB) = n(A - B) + n(B - A) + n(A⋂B)
- n(A - B) = n(A∪B) - n(B)
- n(A - B) = n(A) - n(A⋂B)
- n(A
^{'}) = n(∪) - n(A)

### Other Important Sets Formulas

- n(U) = n(A) + n(B) + - n(A⋂B) + n((A∪B)
^{'}) - n((A∪B)
^{'}) = n(U) + n(A⋂B) - n(A) - n(B)

Let us have a look at a few solved examples to understand the sets formulas better.

## Solved Examples Using Sets Formulas

**Example 1:** In a club, each person plays chess or carrom or both. The number of people who play chess, carrom or both are 11, 12 and 3 respectively. Find the people who play either chess or carrom?

Solution:

Let n(chess)= n(P) and n(chess) = n(Q)

Then we have n(either chess or carrom) = n(P∪Q) and n(chess and carrom) = n(P∩Q)

Given n(P) = 12 , n(Q) = 12 and (P∩Q) = 3

Applying the set formula, n(P∪Q) = n(P) + n(Q) - n(P∩Q) = 11 + 12 - 3 = 20

**Answer: The number of people who play both chess or carrom = 20**

**Example 2:** In a class of 70 students, 45 students like to play soccer, 52 students like to play baseball. All the students like to play at least one of the two games. Using sets formula find how many students like to play soccer or baseball ? How many students like to play only soccer?

**Solution:**

Given: n(A U B ) = 70, n(A) = 45, n(B) = 52

We are required to find n (A ⋂ B)

Using sets formula, n(A ⋂ B)= n(A) + n(B) - n(A ∪ B)

n(A ⋂ B)= 45 + 52 - 70 = 27

Students who like to play only Soccer = 45 - 27 =18

**Answer: 18 students like to play only soccer.**

Example 3: There are 100 students, 35 like painting and 45 like dancing, and 10 like both. How many of the students like either of them or neither of them?

**Solution:**

Total number of students = 100

Number of students that like painting, n(P) = 35

Number of students that like dancing, n(D) = 45

Number of students who like both, n(P∩D) = 10

We are required to find n(A ∪ B) i.e., number of students who like either of them and

Using sets formula, n(P∪D) = n(P) + n(D) – n(P∩D)

⇒ 45 + 35 - 10 = 70

Number of students who like neither = Total students – n(P∪D) = 100 – 70 = 30** **

**Answer: 70 students like either of them and 30 students like neither of them.**

## FAQs on Sets Formulas

### What Is the Formula of Sets?

The set formula is given in general as n(A∪B) = n(A) + n(B) - n(A⋂B), where A and B are two sets and n(A∪B) shows the number of elements present in either A or B and n(A⋂B) shows the number of elements present in both A and B.

### What Is the Formula of an Intersection of Sets?

The set formula for the intersection of two sets A and B is denoted by ⋂. n(A⋂B) means the elements common to both sets A and B. n(A⋂B) = n(A) + n(B) - n(A∪B)

### What Are the Applications of the Sets Formulas?

Set formulas have a wide range of applications in many abstract concepts. For example, if R is the set of real numbers and Q is the set of rational numbers, then R-Q= the set of irrational numbers. The theory of Probability adopts the rules of sets. For instance, the sample space is the universal set. If A and B are two mutually exclusive events P(A∪B) = P(A) + P(B) - P(A⋂B).

### What Is the Cartesian Product Formula on Sets?

If A and B are two sets, their Cartesian Product is the set of ordered pairs of elements of set A and set B. A × B = {(x,y) / x ∈ A and y ∈ B}