How to learn to count quickly in the mind

For quick counting in the mind, you do not need any special knowledge or abilities, the main thing is to constantly train and comply with the rules of counting. Thanks to such training, one can learn to count operations with two-digit and three-digit numbers in the head without much effort.

Instruction manual

one

When adding up multi-valued terms, add the leading digit of a smaller number, then the lower digit. For example, when adding a two-digit number, tens are added first, then units are added. When adding two-digit numbers, first add all tens, then all units, then add units to the total number of tens.

2

When subtracting multi-valued numbers, first subtract the high-order bits of the subtracted, then its low-order bits. To learn how to quickly count in the mind, you need to remember that if the deductible is close in value to the round number, then you must first subtract this round number, and then make the correction.

3

When multiplied by a number that is represented by a unit with zeros, for example, 10 or 100, you need to assign to the multiplier number as many zeros as the multiplier has. When dividing by a number, which is represented by a unit with zeros, it is necessary to separate as many final digits as the number of zeros of the divisor with a comma.

4

To learn how to quickly count in the mind, you need to remember that multiplying the number by 4, you must first multiply it by 2, then again by 2. For example, 214x4 = 428x4 = 856. When dividing by 4, first divide the number by 2, then again by 2. For example, 116: 4 = 58: 2 = 29.

5

When dividing by 8 or 16, you need to 3 or 4 times sequentially divide the number by 2. For example, 448: 8 = 224: 4 = 112: 2 = 56.

6

If you multiply by 25, multiply the number by 100 and divide by 4. If you divide by 25, multiply the number by 4 (2 times by 2) and divide by 100.

7

When multiplying the number by 50, multiply the number by 100 and divide in half, when dividing the number by 50, first double the number, then divide by 100.

eight

When multiplying a number by 9 or 11, increase it 10 times, then subtract this number from the resulting number. For example, we multiply 87 by 11: increasing 87 by 10 times, we get 870, we add 87 to this number, we get 957.