The Interactive Binary Addition Lesson!

Learn how computers add numbers. This is a 20-30 minute interactive lesson.

Part 1: Odd & Even Numbers (5 mins)

A computer can instantly tell if a number is odd or even. It's all about the **last bit** (the "1s" column).

  • If the last bit is a 0, the number is **EVEN**.
  • If the last bit is a 1, the number is **ODD**.

Part 2: The Rules of Addition (5 mins)

To add binary numbers, you add one column at a time (right to left), just like in decimal. There are 5 simple rules to remember.

The 5 Rules:

  • Rule 1: 0 + 0 = 0
  • Rule 2: 0 + 1 = 1
  • Rule 3: 1 + 0 = 1
  • Rule 4: 1 + 1 = 0, Carry 1
  • Rule 5: 1 + 1 + 1 = 1, Carry 1

Worked Example:

Let's add 0011 (3) + 1000 (8):

  C  
  0011
+ 1000
  1011

Result: 1011 (which is 8 + 2 + 1 = 11). It works!

Part 3: 4-Bit Addition (10 mins)

Add the numbers. Type your answer in the box. One attempt only!

Part 4: 8-Bit Addition (10 mins)

Same rules, just more bits! Work right to left. One attempt only!

Part 6: Binary Puzzles (Drag & Drop)

Now for a challenge! Drag the numbers to solve the puzzles.

0110
0010
0100
1000
Drop two numbers here
1000
0111
0110
0101
Drop two numbers here
0001
0011
0101
0100
Drop two numbers here
1000
0111
0110
1001
Drop two numbers here
0011
0100
0110
0101
Drop two numbers here

Part 7: Overflow Errors & Concepts (5 mins)

What happens when the answer is too big? An 8-bit number can only hold values up to 255 (which is 1111 1111). If the answer is 256 or more, it causes an Overflow Error because the 9th bit has nowhere to go!

Hint: The answer is 9 bits long (1 1000 1011). An 8-bit computer can't store it!

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