In the last article in this series on Mental Arithmetic we considered the problem of adding double-digit numbers.

The scope of mental arithmetic is now extended this to the topic of “number bonds” – which are the various ways in which a number can be divided up into two parts which then can be added together to get back to the number.

So number bonds are really the opposite of addition, since in addition we add two numbers to get a single number, and with number bonds we take a single number and then divide it into two smaller numbers.

This is an important part of early mathematics development and it is essential that this is imprinted into your brain as facts, so that you do not need to use a procedure for counting, since procedures take more brain work and slow you down.

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In the last article you added single-digit numbers, such as

• 4+5 (which adds to 9, a single-digit answer), and
• 7+8 (which sums to 15, being larger than 10, a two-digit answer).

I mention again that these two types of single-digit addition are at the core of mental mathematics.

In this article, I extend this to the addition to double-digit numbers, such as 11+32 (which sums to less than 100), and 45+78 (which has a value larger than 100).

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In the first article I talked about how important it is to master mental mathematics so that this can help you through both school and in life situations.

In this article I help you to take the first step of mental mathematical knowledge, which is to memorize the addition of single-digit numbers – being the numbers 0-9. When two of these single-digit numbers are added the value is a number in the range 0-18.

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In this age of the calculator, why should you have to learn to do arithmetic in your head?

Surely the reason that we have the calculator is to help us do our calculations, and it is a tool for all of mankind, including school children, just like the motor car is a tool to get us from one place to another to save on walking.

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