Boolean algebra and logic circuits — AS & A Level Computer Science (9618) questions by topic
Describing how a 2-input XOR gate or a NAND, NOR or OR gate operates, and writing the Boolean expression for a multi-gate circuit with three inputs, sit at the core of this topic, worth 3 to 10 marks across 29 real questions from 2023 to 2025 papers.
Draw, complete, write, express and use lead the command words, and draw means producing a circuit with standard syllabus gate symbols wired unambiguously to the correct inputs, not an approximate sketch. Examiners report precise misreadings of bracket nesting in expressions, so drafting the circuit or expression and checking it against instant marking is the fastest way to confirm the logic was parsed correctly, inside-out.
What examiners look for
- A recurring criticism is misreading nested brackets, for example drawing NOT applied to a whole XOR sub-expression when the expression places NOT on a single input.
- Examiners note the final inverting NOT gate sometimes omitted entirely, leaving the circuit one gate short of the full expression.
- Reports flag expressions selected without checking every row of the truth table, for example missing that two separate input patterns both give an output of 1.
- Strong candidates parsed expressions strictly inside-out, applying NOT to a single input first, then combining terms, then inverting the whole result last, and drew clean, separated standard gate symbols with unambiguous wiring.
May–June 2025, Paper 11
Write the logic expressions for the following logic circuit. The circuit has four inputs P, Q, R and S on the left and two outputs X and Y on the right. Upper section (output X):…
Answer this question and get it marked →May–June 2025, Paper 12
Write the logic expressions for the following logic circuit. The circuit has four inputs R, S, T and U and two outputs X and Y. - Inputs R and S feed into a NOR gate; the output…
Answer this question and get it marked →May–June 2025, Paper 13
Write the logic expressions for the following logic circuit. The circuit has four inputs A, B, C and D on the left and two outputs X and Y on the right. Inputs A and C feed a NOR…
Answer this question and get it marked →May–June 2025, Paper 31
This truth table represents a logic circuit. A B C D Z --- --- --- --- --- 0 0 0 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1 0 0 1 0 0 0 0 1 0 1 1 0 1 1 0 0 0 1 1 1 1 1 0 0 0 1 1 0 0 1 0 1 0…
Answer this question and get it marked →May–June 2025, Paper 32
The diagram shows a logic circuit. Inputs A, B, C, D feed the circuit as follows: - Gate Q is a NOR gate with inputs A and B, producing output Q. - Input C feeds a NOT gate…
Answer this question and get it marked →May–June 2025, Paper 33
This truth table represents a logic circuit. A B C D Z --- --- --- --- --- 0 0 0 0 0 0 0 0 1 0 0 0 1 0 1 0 0 1 1 1 0 1 0 0 1 0 1 0 1 0 0 1 1 0 0 0 1 1 1 0 1 0 0 0 0 1 0 0 1 0 1 0…
Answer this question and get it marked →May–June 2024, Paper 11
Tick (✓) one box to identify the correct logic statement for this truth table. A B C X --- --- --- --- 0 0 0 1 0 0 1 0 0 1 0 0 0 1 1 0 1 0 0 0 1 0 1 0 1 1 0 1 1 1 1 0 Options: [ ]…
Answer this question and get it marked →May–June 2024, Paper 12
Describe the operation of each of the following logic gates: NAND NOR XOR OR
Answer this question and get it marked →May–June 2024, Paper 13
Each of the following truth tables has three inputs (A, B and C) and one output (X). Draw one line to match each truth table with its logic expression. Truth table 1: A B C X ---…
Answer this question and get it marked →May–June 2024, Paper 31
The diagram shows a logic circuit with three inputs, A, B and C, and one output, Z. The circuit contains: - a NOT gate with input B, whose output is labelled P - an AND gate with…
Answer this question and get it marked →May–June 2024, Paper 32
The diagram shows a logic circuit with three inputs A, B and C and one output Z. - Input A passes through a NOT gate to give signal P. - Input B passes through a NOT gate to give…
Answer this question and get it marked →May–June 2024, Paper 33
Complete the truth table for the given logic circuit. Show your working. The columns P, Q, R and S are provided as working space; complete these and the output column Z. A B C P Q…
Answer this question and get it marked →October–November 2024, Paper 12
Complete the truth table for the logic expression: X = (A XOR B) NAND (A AND (B XOR C)) A working space column is provided. Complete the X column. A B C Working space X --- ---…
Answer this question and get it marked →October–November 2024, Paper 13
Describe the operation of a 2-input XOR gate.
Answer this question and get it marked →October–November 2024, Paper 31
Write the Boolean logic expression that corresponds to the given truth table as the sum-of-products. T = ...
Answer this question and get it marked →October–November 2024, Paper 32
Write the Boolean logic expression that corresponds to the given truth table as the sum-of-products. X = ............ (A bar over a variable denotes NOT; a dot denotes AND; a plus…
Answer this question and get it marked →October–November 2024, Paper 33
Write the Boolean logic expression that corresponds to the given truth table as the sum-of-products. T = ............................................
Answer this question and get it marked →May–June 2023, Paper 11
Draw the logic circuit for this logic expression: T = (NOT A OR B) XOR (C NAND D) The question provides a blank rectangular drawing area with four input lines labelled A, B, C and…
Answer this question and get it marked →May–June 2023, Paper 12
Draw the logic circuit for this logic expression: Z = (R XOR S) AND (NOT T NOR P) The answer space provides four input lines labelled R, S, T and P on the left and one output line…
Answer this question and get it marked →May–June 2023, Paper 13
Write the logic expression for this truth table: A B C X --- --- --- --- 0 0 0 1 0 0 1 1 0 1 0 0 0 1 1 0 1 0 0 1 1 0 1 1 1 1 0 0 1 1 1 0
Answer this question and get it marked →May–June 2023, Paper 31
Complete the Karnaugh map (K-map) for the following Boolean expression. Z = A'.B'.C'.D' + A'.B'.C'.D + A'.B.C'.D' + A'.B.C'.D + A.B.C'.D' + A.B.C'.D (where X' denotes NOT X, i.e.…
Answer this question and get it marked →May–June 2023, Paper 32
The given truth table (with inputs A, B, C, D and output Z) represents a logic circuit. Write the Boolean logic expression that corresponds to the given truth table as the…
Answer this question and get it marked →May–June 2023, Paper 33
Complete the Karnaugh map (K-map) for the given Boolean expression. The K-map is a blank 4x4 grid. The columns are labelled AB with values 00, 01, 11, 10 across the top; the rows…
Answer this question and get it marked →October–November 2023, Paper 11
Complete the truth table for the logic expression: X = NOT (A NAND B) XOR (NOT B AND (B NOR C)) A working space column is provided in the question paper. Complete the X column. A…
Answer this question and get it marked →October–November 2023, Paper 12
Write the Boolean expression that corresponds to the following logic circuit. The logic circuit has three inputs, A, B and C. Inputs A and B feed a NAND gate at the top. Input B…
Answer this question and get it marked →October–November 2023, Paper 13
Complete the truth table for the logic expression: Y = ((P AND Q) XOR ((NOT Q) OR R)) AND NOT P A working space column is provided. Complete the Y column. P Q R Y --- --- --- ---…
Answer this question and get it marked →October–November 2023, Paper 31
This diagram represents a logic circuit (inputs A, B, C, D and output Z). Complete the truth table for the given logic circuit. (A 'Working space' column is provided on the…
Answer this question and get it marked →October–November 2023, Paper 32
This logic circuit represents the Boolean expression: X = NOT(A + B + C) (The logic circuit is a single three-input NOR gate: inputs A, B and C enter an OR-gate shape whose output…
Answer this question and get it marked →October–November 2023, Paper 33
This diagram represents a logic circuit. Complete the truth table for the given logic circuit.
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