**How to Do Mental Math Without a Calculator or Paper**
How to calculate in your head? If you ask me why this is necessary, I’ll tell you: you might find yourself in a situation where you need to perform calculations, but you don’t have a calculator or even a pen and paper at hand. Anyone, whether a top student or a struggling one, can learn how to calculate mentally, claims https://xrust.ru/.
**Break numbers into parts**—hundreds, tens, and ones—and perform calculations with them. For example:
712 + 281 → “700 + 200,” “10 + 80,” and “2 + 1.”
700 + 200 = 900, then 10 + 80 = 90, and finally 2 + 1 = 3.
900 + 90 + 3 = 993.
Use “hundreds” or “tens” instead of single-digit numbers. For example, turn 37 + 45 into “30 + 40 = 70” and “7 + 5 = 12.” Then add 70 + 12 to get 82. Learn to add multiple numbers at once.
**Rearrange numbers** to create convenient sums. The calculation remains the same regardless of the order in which it’s solved. For example:
7 + 4 + 9 + 13 + 6 + 51 can be rearranged into (7 + 13) + (9 + 51) + (6 + 4) = 20 + 60 + 10 = 90.
**Multiply left to right.**
On paper, most people multiply digits starting from the rightmost position. But mentally, it might be easier to work from left to right. For example:
For 453 x 4, start with 400 x 4 = 1600, then 50 x 4 = 200, and finally 3 x 4 = 12. Add them all together to get 1812.
If both numbers have multiple digits, you can break them into parts. Each digit needs to be multiplied by every other digit, so it can be hard to keep track of all the numbers. For example:
34 x 12 = (34 x 10) + (34 x 2), which can be broken down into (30 x 10) + (4 x 10) + (30 x 2) + (4 x 2) = 300 + 40 + 60 + 8 = 408.
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