Mental Subtraction

Mental Subtraction is similar to Mental Addition with a bit of deviation.

The steps to compute the answer to the subtraction is still the unconventional left-to-right approach. This allows the answer to the mental subtraction to be recalled straight from the left digit.

We can do an example using the left-to-right approach.

5 4 3
3 2 2 -
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We start from left digit by doing 5 - 3 = 2, next, the centre digit 4 - 2 = 2,
and finallyright digit 3 - 2 = 1==> Answer is 221.

You can get this with the conventional right-to-left approach but need to flip the final answer to get 221.

How about this subtraction which is a bit more challenging?

4 0 0
3 1 6 -
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This calls for a bit of deviation and creativity.

Mental maths operation lies in simplification to achieve speed. In the above last question, we can actually simplify the 316 by splitting it to 300 + 10 + 6.

This makes the mental subtraction easier in that the first subtraction deals with a simplier number of 300.

Later the answer is followed by subtracting 10 and lastly subtracting 6.

400 - 300 = 100
100 - 10 = 90
90 - 6 = 84
That is the final answer !

See how amazingly simple mental subtraction can be when simplified.

Another example of mental subtraction (with deviation)
4 0 0
2 9 4 -
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For this question, we note that 294 is very close to 300.

So we mentally subtract using the 300 ==> 400 - 300 = 100

But since we over-subtract by 6, we return 6 to the above subtracted answer
===> 100 + 6 = 106.
That it, the final answer done mentally!