iGCSE Computer Science - Distance Learning

Tutor Marked Assignment 6
Tutor Marked Assignment 8 (Programming)

Adding Binary Numbers (2023 Specification Only)

New 2023 Syllabus Only

Adding binary numbers uses the concept of long addition that you should already be familiar with from maths. There are just four rules that you need to remember:

0 + 0 = 0 (zero)
0 + 1 = 1 (one)
1 + 1 = 10 (two)
1 + 1 + 1 = 11 (three)

Task: As you complete this lesson, create notes using the Scribbl.it file below. These work best when printed and completed by hand – adding notes in colour will help you to remember the key terms.

How To Add Binary Numbers

Adding binary numbers requires us to remember four rules and that we’re actually only adding denary numbers:

0 + 0 = 0

1 + 0 = 1

1 + 1 = 2 (or 10 in binary)

1 + 1 + 1 = 3 (or 11 in binary)

These first two rules are nice & simple because when you write out a binary number, there’s no need to carry a 1. When we get to the second two rules, we apply the same techniques that we use in long addition in maths.

How Computers Deal With Overflow

When the result of a binary addition ends up with a number that has more bits than the numbers being added, this is called an overflow error. In the video, I highlighted this by drawing a box around the number and crossing it through. This technique is called signposting and helps you to tell the examiner your thought processes (it’s like shouting at them “Give Me The Marks!!”).


Once you have completed the video lesson at the top of the page, download this practice sheet and test your understanding of adding Binary numbers. Use the second page to check your answers.