## CS Unplugged: binary numbers

Materials: Print off several sets of the following pages: dotPages.doc (enough for one card per student).
Resources: http://www.csunplugged.org/binary-numbers

Group students into groups of 5. Tell them how to make numbers by holding cards face-up or face-down and adding the dots on the pages. For example, have them make 5 by showing the card with 4 dots and the card with 1 dot.

Have them make 7, 3, 15, and 9. Then have them start counting up and see how many numbers they can make with the 5 cards. Point out that the card with 1 dot flips the most and the one with 16 dots the least.

Then challenge them to count to more than 5 with the fingers on one hand (they can count from 0 to 31 if they think of the fingers as representing the cards). You can have one person show the binary equivalent on the board when the others are working with the cards.

Tell the students that computers represent numbers by groups of binary digits. Ask how they think computers represenent negative numbers, letters, and floating point numbers.