How to count in the mind without a calculator and paper

how to count in the mind? If you ask me the question, why is this necessary? I will give an answer: you may find yourself in a situation where you need to complete the calculations, but you do not have a calculator or even handles with paper.

How can an excellent student and double can understand, says Xrust.

Break the numbers into separate parts — by hundreds, dozens, units and perform actions with them. For example:

• 712 + 281 → «700 + 200», «10 + 80» and «2 + 1»
  700 + 200 = 9 00 = 9 0, then 2 + 1 = 3
  900 + 90 + 3 = 993; Style = «Text-align: Justify;»> Use «hundreds» or «tens» instead of unambiguous numbers. For example, turn 37 + 45 into “30 + 40 = 70” and “7 + 5 = 12”. Then add 70 + 12 and get 82.

Learn to fold many numbers at the same time.
Rinse the numbers to get convenient amounts. The task of addition remains unchanged regardless of the order of its decision.
For example, 7 + 4 + 9 + 13 + 6 + 51 can be converted into (7 + 13) + (9 + 51) + (6 + 4) = 20 + 60 + 10 = 90.

Multiple most people. But in the mind it can be easier to act the opposite: from left to right. For example:

• For 453 x 4, start with 400 x 4 = 1600, then 50 x 4 = 200, then 3 x 4 = 12. Fold them all together to get 1812;
• If both numbers are numb They consist of several digits, they can be divided into parts. Each figure needs to be multiplied by every other, so it may be difficult to keep track of all numbers. For example: 34 x 12 = (34 x 10) + (34 x 2), which can be divided into (30 x 10) + (4 x 10) + (30 x 2) + (4 x 2) = 300 + 40 + 60 + 8 = 408.

Xrust how to count in the mind without a calculator and paper