# How to learn to quickly calculate?

It would seem, to whom in our time moderntechnologies need this skill? After all, you can always take a calculator, which is available in any mobile phone, and make the necessary calculations. However, sometimes the desired device may not be near. There will be a useful ability to quickly count in the mind.

There is a definite set of arithmeticalgorithms, each of which in one way or another makes it possible to significantly simplify the account. Beginning to learn a quick account in the mind is necessary with the memorization of these algorithms.

## Subtraction 7, 8, 9

If you need to subtract from any number 9, 8 or 7, subtract 10 from it, and then add 1, 2 or 3 respectively. For example: 52-9 = 52-10 + 1 = 43.

## Multiplication by 9

To multiply any number by 9, multiply it by 10, that is, just add zero at the end, and then subtract the first multiplier from the result (that is, the number that we multiply).

For example, 72 * 10 (= 720) - 72 = 648.

## Multiplication and division by 2

This, it would seem, is a very simple action, butwhen it comes to large numbers, everything becomes complicated. It is especially problematic to multiply non-round numbers. 150 multiplied by two is very simple, but 146 is much heavier. In this case, we round 146 to 150, multiply, and then subtract the difference between rounded and non-rounded numbers multiplied by two. I.e:

- 150 * 2 (= 300) - 4 * 2 = 292.

Do the same in dividing:

- 150/2 = 75
- 75-4 / 2 = 67.

## Division and multiplication by 4 and 8

Division and multiplication by 4 and 8 are respectively doubled and quadrupled division and multiplication by two, so that it is better to perform these actions sequentially. That is: 16 * 4 = 16 * 2 (= 32) * 2 = 64.

## Multiplication by 5 and 25

To quickly multiply by five, multiply the number by 10, and then divide it in half. For example: 25 * 5 = 25 * 10 (= 250) / 2 = 125.

To multiply by 25, divide the number by four, and then multiply it by 100. For example: 16 * 25 = 16/4 (= 4) * 100 = 400.

## Multiplication by single-valued numbers

To quickly multiply any number by a single digit, it is convenient to perform a sequential multiplication. For example: 84 * 8 = 80 * 8 (640) + 4 * 8 (32) = 672

or 153 * 6 = 100 * 6 (600) + 50 * 6 (300) + 3 * 6 (18) = 918.

## conclusions

Of course, at first glance, these algorithms canseem to you too zamorochennymi, in addition, you can even think that some of the actions much faster can be done without using them. However, this is only so long as your actions on the algorithm are not brought to automaticity.

More lessons you can find here - 4brain.ru. Also read the additional information in our article How to learn to count.