A lot of people have the attitude that calculators free a person from the need to do tedious number crunching, and therefore mental arithmetic is unnecessary. It is certainly true that use of calculators makes it possible to concentrate on advanced mathematical skills. I would argue though that practice in mental arithmetic helps reinforce what is being taught and may even help prepare a student to learn new material.

For example, ask someone to mentally compute 999 * 999. On the face of it, this seems extremely difficult, but if you think of it as (1000 – 1)(1000 – 1), it becomes doable. You get 1000^2 – 2000 +1 = 998,001. This is a nice way of reinforcing the basic algebra formula (x – y)^2 = x^2 – 2xy + y^2. What is 16 * 16? Think of this as 16 * (2*2*2*2). Doubling 16 four times gives 32, 64, 128 and finally 256. A student in elementary school could do this, and it will facilitate teaching the law of exponents later on, that is, x^a * x^b = x^(a+b).

How can mental arithmetic be encouraged? A teacher could simply challenge a class to solve a problem in their heads. It could be a good way of reviewing old concepts or introducing new ones.