Using one’s hands is practically intuitive in the math world. Counting on one’s fingers is the most basic mathematical practice one could think of. But there is other more complex math you and your kid can do with your hands!
For example, you are hardly limited to counting to 10. If you bring the binary system into the equation, your kid can count all the way to 1,023 using their hands. It’s pretty simple: 0 is your right fist, 1 is your right thumb, 2 is your right index finger, and 4 is your right middle finger. Do you see a pattern? Each finger number is the double of the one before it. So, if you want to count 6, you hold up your index and middle finger (2 and 4). A more thorough explanation is in comic form at Instructables.
In addition to counting on your hands, you can also use them as multiplication tables. Ms. K at Teacher Blog Spot explains how your kid can divide each finger into sections of 3 or 4 and multiply by the number of fingers, with a maximum of either 15 or 20.
A similar method of multiplying on your fingers is called finger reckoning. Finger reckoning has been used since at least the 15th century, when merchants would use it to calculate numbers out of the sight of competitors eyes. While Ms. K’s method is based primarily on counting, finger reckoning uses multiples of ten. It is more complex but you get the answer faster and more efficiently. You can read more about finger reckoning in our blog post about it.
There’s no need to limit you or your kid to computing multiplication and addition, however. An easy and useful trick for remembering how many days are in each month is to count out the months on your knuckles and the spaces in between. Make sure to remember that each knuckle is 31 days and each space is 30 days, except February, which is 28 or 29.
Hand tricks aren’t limited to computation either. One of the most common practices in kid art is tracing hands for drawings, and that can be used to teach symmetry. While we didn’t come up with this particular example, the Moebius Noodles book has a symmetry game called Double Doodle Zoo which demonstrates how one shape (like the hands) can turn into another (the heart).
An easy three-dimensional example of a hand shape is getting a few people together and having them recreate a fibonacci spiral with their hands. This is a great example of shapes in math and how they can transcend two dimensions.
You can do even more geometry with your body than making a Fibonacci spiral with your hands. In this video, mathemetician James Tanton explains how to do the National Math Salute. Using knot theory, you create a simple knot with your hands and undo it. The hand salute also uses elements of topology: the study of insides and outsides, and the orientation of surfaces. It’s simple to watch, but it’s easy to do it wrong. See if you and your kid can figure it out!