Understanding Binary Numbers - 2025

• Computing
• Lower Secondary (Key Stage 3)

What do all these things have in common?

Talking points:

All represent on/off or two-state systems.

Binary uses this same idea to represent numbers in computers.

Support: Provide key words (on/off, power, pattern, digit).

Challenge: “How do computers use on/off signals to store information?”

To understand how binary numbers are used to represent data in computers.

All: Explain that computers use binary (1s and 0s) to represent data.

Most: Convert between binary and decimal numbers up to 8 bits.

Some: Explain why binary is essential and accurately convert both ways beyond 8 bits.

How can we count from 0 - 31 on one hand?

Play from 0:00 - 01:30

What is the highest number you can count to on one hand?

1. 5 – Each finger represents one number.
2. 10 – Counting each finger as two parts (knuckle and tip).
3. 31 – Using binary, each finger is a bit (2⁵ – 1).
4. 100 – If you count rapidly using finger movements.

Why does each finger have a different value when counting in binary?

1. Because each finger represents a different power of 2 (1, 2, 4, 8, 16).
2. Because some fingers are longer than others.
3. Because the dominant hand is stronger and can count more.
4. Because each finger stands for a random number we choose.

How is binary counting on your fingers similar to how computers store numbers?

1. Computers store numbers by counting on five fingers internally.
2. Computers use random numbers and choose whichever is fastest.
3. Computers store numbers by writing the value in words (e.g., “twenty-five”).
4. Each finger (on/off) is like a bit (1/0) that represents powers of 2.

Binary vs Decimal Systems

Binary (Base 2): 0 and 1 Decimal (Base 10): 0–9 Example: 1011₂ = (8 + 0 + 2 + 1) = 11₁₀

How many characters make up the binary number system?

2 (base 2)

8 (base 8)

10 (base 10)

16 (base 16)

Why can’t computers use Base 10?

04:09

What is the binary number 101 in denary?

1. 101
2. 50
3. 5
4. 10

04:27

What is the binary number 10011 in denary?

1. 5
2. 91
3. 50
4. 19

Your turn - Worksheet

Complete the  worksheet. Your teacher will give you a printed copy.

Here is a link to download the worksheet...

💻 The Ten-Minute Binary Challenge

🔗 Play here: https://learningcontent.cisco.com/games/binary/index.html

🕹️ Instructions

1️⃣ Start with Level 1 to practise conversions.

2️⃣ Progress through levels as your confidence grows.

3️⃣ Try to beat your own score or compete with a partner.

4️⃣ The three students with the highest score will receive a ViPO for Independence! 🏅

Binary Bingo!

Convert the binary number 01010101 into denary.

(You can use the mini whiteboard in your planner for working out)

Binary Bingo!

Convert the denary number 37 into binary (8 bit byte) ...

(You can use the mini whiteboard in your planner for working out)

Binary Bingo!

Convert the denary number 127 into binary (8 bit byte) ...

(You can use the mini whiteboard in your planner for working out)

Review - Why Binary?

Why do computers use binary?
What does each bit represent?
How is binary like the light switch in the starter?

Extension

Research how binary connects to:

• images (pixels)
• sound (sample rate)
• colours (bit depth)