We created the Web Sketchpad game below (and here) as part of our Dynamic Number project. It challenges elementary-age students to uncover the value of a secret number by collecting and analyzing clues that narrow its range of possible values. The game familiarizes students with inequality signs, introduces the use of *x* to represent an unknown value, and motivates students to develop strategies for finding the secret number in as few guesses as necessary.

There are seven variants of the game. Use the arrows in the lower-right corner of the game to move from one version to the next.

The video below the game provides a short introduction to the game.

*An annotated list of all our elementary-themed blog posts is here.*

Interesting! but what about a number between 4 and 5? You probably should say a whole number between 0 and 5. An extension would be a number between 4 and 5. This is tricky because you can make it difficult by using many decimal digits. I found the decimal extension to be fun for kids (in my case 6 graders) as long as my answer had a reasonable number of digits starting with say 4.3 then going to the hundredths place and so on…

I love what you are doing with the elementary project!

Extending this number line model to decimals is a really nice idea! Makes me think of our “zooming” decimal model where students repeatedly magnify intervals on a number line to make better estimates of a point’s location.