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A-LevelComputer ScienceHardware9618/12 · Oct/Nov 2025 · Q94 Marks

Consider the following logic circuit: [Logic circuit diagram with inputs A, B, C and output X] Write the logic expression for the logic circuit. Do not simplify the expression. X =

  1. (a)Consider the following logic circuit: [Logic circuit diagram with inputs A, B, C and output X] Write the logic expression for the logic circuit. Do not simplify the expression. X =[2]
  2. (b)Consider the following logic expression: X = NOT ((A NAND B) XOR (NOT A OR NOT C)) A truth table for the logic expression is given: Row number A B C X 1 0 0 0 1 2 0 0 1 0 3 0 1 0 1 4 0 1 1 0 5 1 0 0 1 6 1 0 1 0 7 1 1 0 1 8 1 1 1 1 There are three errors in the truth table. Identify the three errors in the truth table by writing the row numbers with an incorrect output. Error 1 Row number .................................................... Error 2 Row number .................................................... Error 3 Row number ....................................................[2]

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Mark scheme

Marking points from the official mark scheme (Oct/Nov 2025). The mark or mark type is shown in brackets.

  1. 9(a) 1 mark per bullet point, max 2 marks
  2. NOT (A XOR B)
  3. NAND ((B AND C) OR A)
  4. X = (NOT (A XOR B)) NAND ((B AND C) OR A)
  5. // X = ((B AND C) OR A) NAND (NOT (A XOR B))
  6. 9(b) 1 mark for 1 or 2 row numbers correct, 2 marks all three correct
  7. Row 2
  8. Row 4
  9. Row 7

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About this question

Topic
Hardware, A-Level Computer Science (syllabus 9618). Structured question, 4 marks.
Source
A-Level Computer Science, Oct/Nov 2025 Paper 1 Variant 2, question 9.

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