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Subjects · Leaving Cert Computer Science

Leaving Cert Computer Science: Binary & hexadecimal

How often Binary & hexadecimal comes up on the Computer Science papers, every year it was asked, and questions to try.

HL Asked on 4 of the last 5 Higher Level papers, most recently in 2025. most years

OL Asked on 5 of the last 5 Ordinary Level papers, most recently in 2025. banker

Binary & hexadecimal, Higher Level(9 marks)

Quick ones on Binary & hexadecimal.

(a)Convert binary 101101 to denary.
  1. 44
  2. 45
  3. 53
(b)Convert denary 200 to 8-bit binary.
  1. 10011000
  2. 11000100
  3. 11001000
(c)Convert hexadecimal 3F to denary.
  1. 63
  2. 61
  3. 48
Show the answers

(a) 45

(b) 11001000

(c) 63

Your turn: Higher Level questions on Binary & hexadecimal.

Higher Level

Asked on 4 of the last 5 Higher Level papers, most recently in 2025. most years

Every paper, year by year

YearWhere it came up
2025A5
2024A3
2023A2
2022Not asked
2021A2, A8

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

More Binary & hexadecimal questions

Binary & hexadecimal, 3 marks

What is the largest denary number that 3 hexadecimal digits can hold?

  1. 999
  2. 4096
  3. 4095
Show the answer

4095

The largest is FFF = 15 x 256 + 15 x 16 + 15 = 4095. There are 16 x 16 x 16 = 4096 values, but counting starts at 0, so the top one is 4095.

Binary & hexadecimal, 3 marks

How can you tell from its binary form that a whole number is odd?

  1. It has an odd number of 1s
  2. Its rightmost bit is 1
  3. Its leftmost bit is 1
Show the answer

Its rightmost bit is 1

The rightmost column is worth 1 and every other column is even, so only that bit decides odd or even. 10 (2) has one 1 but is even; 110 (6) starts with 1 but is even.

Binary & hexadecimal, 3 marks

Convert hexadecimal 1F4 to denary.

  1. 500
  2. 496
  3. 420
Show the answer

500

1F4 = 1 x 256 + 15 x 16 + 4 = 256 + 240 + 4 = 500. The third hex column from the right is worth 16 x 16 = 256.

Ordinary Level

Asked on 5 of the last 5 Ordinary Level papers, most recently in 2025. banker

Every paper, year by year

YearWhere it came up
2025A3
2024A2
2023A4
2022B13
2021A2

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

More Binary & hexadecimal questions

Binary & hexadecimal, 3 marks

Convert binary 1011 to denary.

  1. 13
  2. 7
  3. 11
Show the answer

11

Place values 8, 4, 2, 1. 1011 = 8 + 0 + 2 + 1 = 11.

Binary & hexadecimal, 3 marks

Convert denary 12 to 4-bit binary.

  1. 0011
  2. 1100
  3. 1010
Show the answer

1100

12 = 8 + 4, so put 1s under 8 and 4 and 0s under 2 and 1: 1100. Check: 1010 is 10 and 0011 is 3.

Binary & hexadecimal, 3 marks

Largest number that fits in one byte (8 bits)?

  1. 255
  2. 256
  3. 128
Show the answer

255

11111111 = 128 + 64 + 32 + 16 + 8 + 4 + 2 + 1 = 255. A byte has 256 values, but they run from 0 to 255.

Other Computer Science topics

All of Leaving Cert Computer Science