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Subjects · Leaving Cert Computer Science

Leaving Cert Computer Science: Logic gates & truth tables

How often Logic gates & truth tables comes up on the Computer Science papers, every year it was asked, and questions to try.

HL Asked on 3 of the last 5 Higher Level papers, most recently in 2024. most years

OL Asked on 4 of the last 5 Ordinary Level papers, most recently in 2024. most years

Logic gates & truth tables, Higher Level(6 marks)

Quick ones on Logic gates & truth tables.

(a)What is the output of an AND gate when its inputs are 1 and 0?
  1. 1
  2. 0
  3. Depends on the last output
(b)Which gate outputs 1 only when its two inputs are different?
  1. NAND
  2. OR
  3. XOR
(c)How many rows (not counting the heading) does a truth table with 3 inputs have?
  1. 8
  2. 9
  3. 6
Show the answers

(a) 0

(b) XOR

(c) 8

Your turn: Higher Level questions on Logic gates & truth tables.

Higher Level

Asked on 3 of the last 5 Higher Level papers, most recently in 2024. most years

Every paper, year by year

YearWhere it came up
2025Not asked
2024A1
2023A3
2022A4
2021Not asked

Links open the State Examinations Commission’s paper for that year.

More Logic gates & truth tables questions

Logic gates & truth tables, 3 marks

A security light should come on only when it is dark and movement is detected. Which gate fits?

  1. OR
  2. XOR
  3. AND
Show the answer

AND

AND outputs 1 only when both inputs are 1. OR would switch the light on in daylight whenever someone walked past.

Ordinary Level

Asked on 4 of the last 5 Ordinary Level papers, most recently in 2024. most years

Every paper, year by year

YearWhere it came up
2025Not asked
2024A6
2023A10
2022A11
2021B15

Links open the State Examinations Commission’s paper for that year.

More Logic gates & truth tables questions

Logic gates & truth tables, 2 marks

An AND gate outputs 1 when…

  1. Either input is 1
  2. Both inputs are 0
  3. Both inputs are 1
Show the answer

Both inputs are 1

AND needs every input on. Its truth table has one 1, in the row where A = 1 and B = 1.

Logic gates & truth tables, 2 marks

An OR gate with inputs 0 and 1 outputs…

  1. 2
  2. 1
  3. 0
Show the answer

1

OR outputs 1 when at least one input is 1. It only outputs 0 when both inputs are 0.

Logic gates & truth tables, 2 marks

A NOT gate with input 1 outputs…

  1. 0
  2. 1
  3. Nothing
Show the answer

0

A NOT gate (inverter) has one input and flips it: 1 becomes 0 and 0 becomes 1.

Other Computer Science topics

All of Leaving Cert Computer Science