Evaluating Boolean expressions: Class 11 practice

What you should know first

• Logic gates

The idea behind evaluating boolean expressions

NOT flips a value, AND is 1 only when both inputs are 1, OR is 1 when at least one is 1. Evaluate NOT first, then AND, then OR (or follow brackets). A truth table lists every input combination.

Step-by-step method

1. Substitute the input values.
2. Apply NOT, then AND, then OR.
3. For a truth table, repeat for all 2ⁿ input rows.

Worked example 1 (Basic)

Evaluate (A + B)·C' for A = 0, B = 1, C = 0.

1. Apply NOT, AND, then OR
2. = 1
3. Answer: 1

Worked example 2 (Standard)

Evaluate (A·B)' + C for A = 0, B = 1, C = 0.

1. Apply NOT, AND, then OR
2. = 1
3. Answer: 1

Worked example 3 (Challenge)

How many of the 8 input rows make (A + B)'·C equal to 1?

1. Evaluate each row (A, B, C from 000 to 111): 01000000
2. Count of 1s = 1
3. Answer: 1

Common mistakes and misconceptions

• Doing OR before AND
• Missing a row in the truth table

Practice questions

1. (Basic) Evaluate A·B + C for A = 1, B = 0, C = 0.
2. (Basic) Evaluate A ⊕ B for A = 0, B = 0, C = 1.
3. (Standard) Evaluate A'·B + A·C for A = 1, B = 0, C = 1.
4. (Standard) Evaluate A'·B + A·C for A = 1, B = 0, C = 0.
5. (Challenge) How many of the 8 input rows make A'·B + A·C equal to 1?
6. (Challenge) How many of the 8 input rows make (A·B)' + C equal to 1?

Answer key with full working

• Q1: Apply NOT, AND, then OR → = 0 → Answer: 0
• Q2: Apply NOT, AND, then OR → = 0 → Answer: 0
• Q3: Apply NOT, AND, then OR → = 1 → Answer: 1
• Q4: Apply NOT, AND, then OR → = 0 → Answer: 0
• Q5: Evaluate each row (A, B, C from 000 to 111): 00110101 → Count of 1s = 4 → Answer: 4
• Q6: Evaluate each row (A, B, C from 000 to 111): 11111101 → Count of 1s = 7 → Answer: 7

Syllabus note

This skill is listed under "Computer Systems and Organisation" for Class 11 in the NCERT/CBSE books. ICSE, IGCSE, IB and state boards may teach it in a different chapter or year.

Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.

Related practice and notes

• Binary ↔ decimal conversion
• Octal and hexadecimal conversion
• Binary addition and two's complement
• Units of memory
• Python arithmetic: //, % and **
• String indexing and slicing
• Tracing loop output
• List operations and methods
• All Class 11 practice

Frequently asked questions

Which chapter is evaluating boolean expressions in?

"Computer Systems and Organisation", Class 11 Computer Science (NCERT/CBSE). Other boards may place it differently.

How were the answers checked?

Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.