Binary: counting with two digits

Ages 9 to 12 Read alone or together · about 35 minutes

Read together

We count with ten digits, 0 to 9. Computers use only two, 0 and 1, because their parts have two states: off and on.

This is called binary. Each place is worth double the one on its right: 1, 2, 4, 8, 16.

In binary, 5 is written 101, because 4 + 0 + 1 = 5.

Do it

1. Make five cards with dots: 16, 8, 4, 2, 1 dots. Put them in a row, largest on the left.
2. To show a number, turn cards face up (1) or face down (0) so the dots add up to it. Show 5, then 9, then 13.
3. Make a binary bracelet: for each of the five places use a light bead for 0 and a dark bead for 1, and spell your age.
4. Write the numbers 1 to 10 in binary and look for patterns.

Talk about it

• What number is 1101?
• Why do computers use only 0 and 1?

For the grown-up

Binary is the base-2 number system. Computers store text, images and sound as long strings of binary digits, or bits. The cards show place value in a new base, which also strengthens understanding of our base-10 system.

Mark as done

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Where this comes from

• Tim Bell, Ian H. Witten and Mike Fellows, Computer Science Unplugged (University of Canterbury, New Zealand), activity “Binary Numbers”
• Charles Petzold, Code: The Hidden Language of Computer Hardware and Software, 2nd ed. (Microsoft Press, 2022)

Written with AI assistance and checked against the sources listed. Please read it before sharing it with a child.