# Lesson 6 – Binary Addition

Learning Objectives

• Understand that computers are digital devices so they use the binary number system
• Be able to add together two binary numbers

Learning Outcomes

All must know that computers are digital and this means that they have to use binary numbers to store information.  With lots of help, add together two binary numbers. (Level 4)

Most should know that computers are digital and be able to explain why therefore computers use binary numbers to store information.  With some help, add together two binary numbers. (Level 5)

Some could explain why computers use binary to store digital information and why binary is useful for computers.  Can confidently add together binary numbers and has completed all of the extension questions. (Level 6)

Keywords

Words to learn: digital, binary, addition, calculation

Starter

Read the page and look at the example on BBC KS3 Computing Bitesize.

Main

In today’s lesson you are going to master the art of adding binary numbers together.  You need to consider the solutions carefully and slowly.  Adding in binary is similar to adding in decimal, but you only have two numbers to work with – zero and one.

You just need to follow the following rules:

Rule 1) Start with the Least Significant Bit (that’s the number furthest on the right)
Rule 2) If you add 0 + 0 then the answer is 0
Rule 3) If you add 0 + 1 then the answer is 1
Rule 4) If you add 1 + 1 then the answer is 0 carry 1 (so the carry is moved to the left)
Rule 5) If you add 1 + 1 + 1 then the answer is 1 carry 1 (so the carry is moved to the left)

Easy?

Print out and try these questions from mrfraser.org which gives you a few to try out – remember to show your working!  Put the answers into your folder once you are finished.

“Like a boss” Extension: Try working out the answers to the following questions – again show your working:

```a) 01011011 + 00011101
b) 01110001 + 00111101
c) 01001011 + 00110110
d) 01010110 + 00101101
e) 10110000 + 11010101
f) 11101111 + 11101101
g) 10011010 + 01110010
h) 11011111 + 00010001
i) 00101011 + 00011101
j) 11010101 + 01000100```

Here’s a “boss question” to think about: Imagine you have a computer that can only store 8 binary digits in a memory location.  What happens if you add two binary numbers and you end up with 9 bits instead of 8 bits?  What solutions can you think of?

Plenary

So you think you’re good at binary now do you?  Have a go at this quiz and see if you can do binary under pressure… click here