Combined Operations on Sets

4.3 Combined Operations on Sets
MATHEMATICS • Form 4 • Chapter 4: Operations on Sets

4.3 Combined Operations on Sets

Combined operations on sets involve performing both intersection and union of sets at the same time. These operations are evaluated from left to right, but any operation enclosed in brackets must always be executed first. This topic also covers finding the complement of combined operations and using Venn diagrams to solve real-world problems.

Learning Objectives

  • Determine and describe combined operations on sets using various representations such as element listing and Venn diagrams.
  • Determine and describe the complement of combined operations on sets using element listing and Venn diagrams.
  • Solve real-world problems involving combined operations on sets using Venn diagrams and algebraic equations.

Step-by-Step Venn Diagram Shading for Combined Operations

See how bracketed operations are shaded first, then combined to obtain the final region.

Step 1: \(P \cup Q\) P Q R

Shade all regions covered by \(P\) or \(Q\).

Step 2: Set \(R\) P Q R

Shade all regions covered by \(R\).

Step 3: \((P \cup Q) \cap R\) P Q R

Shade only the common region between \((P \cup Q)\) and \(R\).

Brief Explanation

Order of Operations for Sets

Combined operations on sets involve both intersection \((\cap)\) and union \((\cup)\) simultaneously. Solve from left to right, but always carry out operations inside brackets first.

Complement of Combined Operations

The complement of a combined set contains all elements in the universal set \((\xi)\) that do not belong to the specified combined set.

1
Solve inside brackets first
For \((P \cup Q) \cap R\), determine \(P \cup Q\) first.
2
Continue from left to right
Then find the intersection of the resultant set with \(R\).
3
Apply the complement
For \((A \cup B)'\), list all elements in \(\xi\) that are not in \(A \cup B\).
4
Shade the Venn diagram
Shade the final region that satisfies the complete combined operation.

Try Answering First

Read the question, answer it in your mind, then press “Check Answer”.

1

If \(\xi = \{1, 2, 3, 4, 5, 6, 7, 8, 9, 10\}\), \(A = \{2, 3, 5, 7\}\), and \(B = \{1, 3, 5, 7, 9\}\), what is \((A \cap B)'\)?

Answer: \(A \cap B = \{3, 5, 7\}\). Therefore, \((A \cap B)' = \{1, 2, 4, 6, 8, 9, 10\}\).
2

Given \(X = \{a, b, c\}\), \(Y = \{b, c, d\}\), and \(Z = \{c, d, e\}\), find the elements of \((X \cup Y) \cap Z\).

Answer: \(X \cup Y = \{a, b, c, d\}\). The intersection of \(\{a, b, c, d\}\) and \(\{c, d, e\}\) is \(\{c, d\}\).
3

In a Venn diagram with sets \(A\), \(B\), and \(C\), which region represents \(A \cap (B \cup C)\)?

Answer: The region of set \(A\) that overlaps with either set \(B\) or set \(C\) (or both).

Worked Examples

The complement of combined operations on sets, and a real-world problem solved step by step.

Example 1: Complement of combined operations on sets

Carry out the operation inside the brackets first, then take its complement, and finally combine it with the other set.

Given \(\xi = \{x : x \text{ is an integer}, 30 \leqslant x \leqslant 40\}\), set \(A = \{x : x \text{ is a multiple of } 3\}\), set \(B = \{x : x \text{ is a number such that the sum of its two digits is odd}\}\) and set \(C = \{30, 32, 35, 39, 40\}\). List all the elements of \((A \cup B)' \cap C\).

1
List each set
\(\xi = \{30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40\}\), \(A = \{30, 33, 36, 39\}\), \(B = \{30, 32, 34, 36, 38\}\), \(C = \{30, 32, 35, 39, 40\}\).
2
Carry out the operation in the brackets
\(A \cup B = \{30, 32, 33, 34, 36, 38, 39\}\).
3
Take its complement
\((A \cup B)' = \{31, 35, 37, 40\}\), that is every element of \(\xi\) that is not in \(A \cup B\).
4
Intersect with \(C\)
The common elements of \(\{31, 35, 37, 40\}\) and \(C\) give \((A \cup B)' \cap C = \{35, 40\}\) — the shaded \(C\)-only region in the diagram below.
A B C ξ 33 36 34, 38 30 39 32 35, 40 31, 37
SetElements
\((A \cup B)' \cap C\)\(\{35, 40\}\)
\(A' \cap (B \cup C)\)\(\{32, 34, 35, 38, 40\}\)
\((A \cap C)' \cup (B \cap C)\)\(\{30, 31, 32, 33, 34, 35, 36, 37, 38, 40\}\)

Example 2: A real-world problem

A residents’ association organises sports competitions. 35 participants join the football competition \((A)\), 24 join table tennis \((B)\) and 13 join badminton \((C)\). 4 participants join both football and table tennis, 8 participants join both table tennis and badminton, and 2 participants join all three competitions. No participant joins badminton and football only. Calculate the total number of participants who join one competition only.

Note: the figures 4 and 8 are the totals of those two-set intersections, so they include the 2 participants who join all three. The “two competitions only” regions must therefore have the 2 subtracted first.

A B C ξ 31 2 14 2 0 6 5
1
Fill in the centre region
2 participants join all three competitions, so the region \(A \cap B \cap C = 2\).
2
Subtract the centre from each two-set intersection
Football and table tennis only \(= 4 - 2 = 2\). Table tennis and badminton only \(= 8 - 2 = 6\). Badminton and football only \(= 0\) (given).
3
Find each “one competition only” region
Football only \(= 35 - 2 - 0 - 2 = 31\). Table tennis only \(= 24 - 2 - 2 - 6 = 14\). Badminton only \(= 13 - 0 - 2 - 6 = 5\).
4
Add them up
Participants who join one competition only \(= 31 + 14 + 5 = 50\).

Common Mistakes

  • ! Performing operations from left to right without solving the bracketed operation first.
  • ! Forgetting to subtract the triple intersection when calculating “two competitions only” or “one competition only” in word problems.
  • ! Confusing the complement symbol \('\) with set subtraction, or misunderstanding \((A \cup B)'\) as \(A' \cup B'\). By De Morgan’s laws, \((A \cup B)' = A' \cap B'\).

Misconceptions

Misconception

The operation \((A \cup B)' \cap C\) means find the complement of \((B' \cap C)\) combined with \(A\).

Correct Fact

The prime symbol applies strictly to the expression inside the bracket: first find the union \(A \cup B\), take all elements outside this union in \(\xi\), and finally find the common elements with \(C\).

Summary

  • Combined operations on sets combine union \((\cup)\) and intersection \((\cap)\).
  • Always solve within brackets first; otherwise, compute from left to right.
  • The complement of a set or combined set includes all elements in the universal set \(\xi\) not in that set.
  • Venn diagrams provide an effective visual tool to shade regions and solve multi-set survey problems.
  • Start filling a three-set Venn diagram from the innermost intersection outwards.

Short Activity

Complete all parts first, then press the check answer button.

A. Objective Quiz

1 Which operation must be carried out first in the expression \(P \cup (Q \cap R)\)?

2 Given universal set \(\xi = \{1, 2, 3, 4, 5\}\), \(A = \{1, 2, 3\}\), and \(B = \{3, 4\}\). What are the elements of \((A \cup B)'\)?

B. Fill in the Blanks

3 Combined operations on sets are solved from left to right, but operations in must be carried out first.

4 For a set \(A\) within the universal set \(\xi\), the complement of set \(A\) is written with the symbol .

C. Drag and Drop: Match Each Set Notation with Its Description

Drag each notation to the correct description. On a phone, tap the answer choice first, then tap the description box.

Set Notation
\((P \cup Q) \cap R\)
\((A \cup B)'\)
\(Q \cup (P \cap R)\)
\((A \cap C)'\)
Description
The common region between the union of sets \(P\) and \(Q\), and set \(R\)CorrectTry againEmpty
All elements in the universal set that do not belong to set \(A\) or set \(B\)CorrectTry againEmpty
All regions covered by set \(Q\) combined with the intersection of sets \(P\) and \(R\)CorrectTry againEmpty
All elements in the universal set except those common to both set \(A\) and set \(C\)CorrectTry againEmpty
 

Key Terms

Combined operations on sets Intersection \((\cap)\) Union \((\cup)\) Complement of a set \((A')\) Universal set \((\xi)\) Venn diagram

Combined Operations on Sets

4.3 Combined Operations on Sets
MATHEMATICS • Form 4 • Chapter 4: Operations on Sets

4.3 Combined Operations on Sets

Combined operations on sets involve performing both intersection and union of sets at the same time. These operations are evaluated from left to right, but any operation enclosed in brackets must always be executed first. This topic also covers finding the complement of combined operations and using Venn diagrams to solve real-world problems.

Learning Objectives

  • Determine and describe combined operations on sets using various representations such as element listing and Venn diagrams.
  • Determine and describe the complement of combined operations on sets using element listing and Venn diagrams.
  • Solve real-world problems involving combined operations on sets using Venn diagrams and algebraic equations.

Step-by-Step Venn Diagram Shading for Combined Operations

See how bracketed operations are shaded first, then combined to obtain the final region.

Step 1: \(P \cup Q\) P Q R

Shade all regions covered by \(P\) or \(Q\).

Step 2: Set \(R\) P Q R

Shade all regions covered by \(R\).

Step 3: \((P \cup Q) \cap R\) P Q R

Shade only the common region between \((P \cup Q)\) and \(R\).

Brief Explanation

Order of Operations for Sets

Combined operations on sets involve both intersection \((\cap)\) and union \((\cup)\) simultaneously. Solve from left to right, but always carry out operations inside brackets first.

Complement of Combined Operations

The complement of a combined set contains all elements in the universal set \((\xi)\) that do not belong to the specified combined set.

1
Solve inside brackets first
For \((P \cup Q) \cap R\), determine \(P \cup Q\) first.
2
Continue from left to right
Then find the intersection of the resultant set with \(R\).
3
Apply the complement
For \((A \cup B)'\), list all elements in \(\xi\) that are not in \(A \cup B\).
4
Shade the Venn diagram
Shade the final region that satisfies the complete combined operation.

Try Answering First

Read the question, answer it in your mind, then press “Check Answer”.

1

If \(\xi = \{1, 2, 3, 4, 5, 6, 7, 8, 9, 10\}\), \(A = \{2, 3, 5, 7\}\), and \(B = \{1, 3, 5, 7, 9\}\), what is \((A \cap B)'\)?

Answer: \(A \cap B = \{3, 5, 7\}\). Therefore, \((A \cap B)' = \{1, 2, 4, 6, 8, 9, 10\}\).
2

Given \(X = \{a, b, c\}\), \(Y = \{b, c, d\}\), and \(Z = \{c, d, e\}\), find the elements of \((X \cup Y) \cap Z\).

Answer: \(X \cup Y = \{a, b, c, d\}\). The intersection of \(\{a, b, c, d\}\) and \(\{c, d, e\}\) is \(\{c, d\}\).
3

In a Venn diagram with sets \(A\), \(B\), and \(C\), which region represents \(A \cap (B \cup C)\)?

Answer: The region of set \(A\) that overlaps with either set \(B\) or set \(C\) (or both).

Worked Examples

The complement of combined operations on sets, and a real-world problem solved step by step.

Example 1: Complement of combined operations on sets

Carry out the operation inside the brackets first, then take its complement, and finally combine it with the other set.

Given \(\xi = \{x : x \text{ is an integer}, 30 \leqslant x \leqslant 40\}\), set \(A = \{x : x \text{ is a multiple of } 3\}\), set \(B = \{x : x \text{ is a number such that the sum of its two digits is odd}\}\) and set \(C = \{30, 32, 35, 39, 40\}\). List all the elements of \((A \cup B)' \cap C\).

1
List each set
\(\xi = \{30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40\}\), \(A = \{30, 33, 36, 39\}\), \(B = \{30, 32, 34, 36, 38\}\), \(C = \{30, 32, 35, 39, 40\}\).
2
Carry out the operation in the brackets
\(A \cup B = \{30, 32, 33, 34, 36, 38, 39\}\).
3
Take its complement
\((A \cup B)' = \{31, 35, 37, 40\}\), that is every element of \(\xi\) that is not in \(A \cup B\).
4
Intersect with \(C\)
The common elements of \(\{31, 35, 37, 40\}\) and \(C\) give \((A \cup B)' \cap C = \{35, 40\}\) — the shaded \(C\)-only region in the diagram below.
A B C ξ 33 36 34, 38 30 39 32 35, 40 31, 37
SetElements
\((A \cup B)' \cap C\)\(\{35, 40\}\)
\(A' \cap (B \cup C)\)\(\{32, 34, 35, 38, 40\}\)
\((A \cap C)' \cup (B \cap C)\)\(\{30, 31, 32, 33, 34, 35, 36, 37, 38, 40\}\)

Example 2: A real-world problem

A residents’ association organises sports competitions. 35 participants join the football competition \((A)\), 24 join table tennis \((B)\) and 13 join badminton \((C)\). 4 participants join both football and table tennis, 8 participants join both table tennis and badminton, and 2 participants join all three competitions. No participant joins badminton and football only. Calculate the total number of participants who join one competition only.

Note: the figures 4 and 8 are the totals of those two-set intersections, so they include the 2 participants who join all three. The “two competitions only” regions must therefore have the 2 subtracted first.

A B C ξ 31 2 14 2 0 6 5
1
Fill in the centre region
2 participants join all three competitions, so the region \(A \cap B \cap C = 2\).
2
Subtract the centre from each two-set intersection
Football and table tennis only \(= 4 - 2 = 2\). Table tennis and badminton only \(= 8 - 2 = 6\). Badminton and football only \(= 0\) (given).
3
Find each “one competition only” region
Football only \(= 35 - 2 - 0 - 2 = 31\). Table tennis only \(= 24 - 2 - 2 - 6 = 14\). Badminton only \(= 13 - 0 - 2 - 6 = 5\).
4
Add them up
Participants who join one competition only \(= 31 + 14 + 5 = 50\).

Common Mistakes

  • ! Performing operations from left to right without solving the bracketed operation first.
  • ! Forgetting to subtract the triple intersection when calculating “two competitions only” or “one competition only” in word problems.
  • ! Confusing the complement symbol \('\) with set subtraction, or misunderstanding \((A \cup B)'\) as \(A' \cup B'\). By De Morgan’s laws, \((A \cup B)' = A' \cap B'\).

Misconceptions

Misconception

The operation \((A \cup B)' \cap C\) means find the complement of \((B' \cap C)\) combined with \(A\).

Correct Fact

The prime symbol applies strictly to the expression inside the bracket: first find the union \(A \cup B\), take all elements outside this union in \(\xi\), and finally find the common elements with \(C\).

Summary

  • Combined operations on sets combine union \((\cup)\) and intersection \((\cap)\).
  • Always solve within brackets first; otherwise, compute from left to right.
  • The complement of a set or combined set includes all elements in the universal set \(\xi\) not in that set.
  • Venn diagrams provide an effective visual tool to shade regions and solve multi-set survey problems.
  • Start filling a three-set Venn diagram from the innermost intersection outwards.

Short Activity

Complete all parts first, then press the check answer button.

A. Objective Quiz

1 Which operation must be carried out first in the expression \(P \cup (Q \cap R)\)?

2 Given universal set \(\xi = \{1, 2, 3, 4, 5\}\), \(A = \{1, 2, 3\}\), and \(B = \{3, 4\}\). What are the elements of \((A \cup B)'\)?

B. Fill in the Blanks

3 Combined operations on sets are solved from left to right, but operations in must be carried out first.

4 For a set \(A\) within the universal set \(\xi\), the complement of set \(A\) is written with the symbol .

C. Drag and Drop: Match Each Set Notation with Its Description

Drag each notation to the correct description. On a phone, tap the answer choice first, then tap the description box.

Set Notation
\((P \cup Q) \cap R\)
\((A \cup B)'\)
\(Q \cup (P \cap R)\)
\((A \cap C)'\)
Description
The common region between the union of sets \(P\) and \(Q\), and set \(R\)CorrectTry againEmpty
All elements in the universal set that do not belong to set \(A\) or set \(B\)CorrectTry againEmpty
All regions covered by set \(Q\) combined with the intersection of sets \(P\) and \(R\)CorrectTry againEmpty
All elements in the universal set except those common to both set \(A\) and set \(C\)CorrectTry againEmpty
 

Key Terms

Combined operations on sets Intersection \((\cap)\) Union \((\cup)\) Complement of a set \((A')\) Universal set \((\xi)\) Venn diagram