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Binary addition, overflow and shifts

OCR GCSE Computer Science (J277) · Computer systems (Paper 1) › Memory and storage › Data storage

Practise Binary addition, overflow and shifts. 12 exam-style questions plus unlimited generated ones on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.

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Add the binary numbers 0101 and 0011. Give your 4-bit answer.
1000

Sample questions

Written for this site in the style of OCR exam questions. They are not taken from real past papers.

Question 1Easy3 marks
(a) What is the result of the binary addition 1 + 1?
Tick (✓) one box.[1]
  • 10
  • 2
  • 11
  • 01
(b) State the effect on the value of a binary number of a left shift of one place.[1]
(c) State the effect on the value of a binary number of a right shift of two places.[1]
Show the answer and mark scheme
(a) Answer: 10
(b)
  • it is multiplied by 2 / doubled
(c)
  • it is divided by 4
Question 2Medium3 marks
(a) Explain what is meant by an overflow error.[2]
(b) State one possible consequence of an overflow error in a program.[1]
Show the answer and mark scheme
(a)
  • the result of a calculation is too large
  • to be stored in the number of bits available, e.g. greater than 255 in an 8-bit register
(b)
  • an incorrect result is stored / displayed / the program crashes / data is corrupted
Question 3Hard3 marks
A student added two 8-bit binary numbers. Their working is shown.
  01101011
+ 00110110
----------
  10000001
The student's answer is wrong because they forgot to include one carry.
(a) Give the correct answer as an 8-bit binary number.[1]
(b) Identify the place value of the column where the student forgot to include the carry.[1]
(c) Convert the two numbers being added and your correct answer into denary to show that your answer is correct.[1]
Show the answer and mark scheme
(a) Answer: 10100001
  • 10100001
(b) Answer: 32
  • 32 (the sixth column from the right)
(c)
  • 107 + 54 = 161

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