Amazing Arithmetic Tricks for Calculating Without a Calculator

Helmut Lange provides clear instructions for mastering mental arithmetic and improving speed. This book covers a wide range of everyday math problems, including addition, subtraction, multiplication, division, and calculating percentages. The author's goal is to help both arithmetic enthusiasts and those who have previously struggled with math.

For instance, one method to mentally calculate 123 divided by 5 is to double 123 to get 246, and then insert a decimal point to get 24.6. Similarly, 123 divided by 9 can be calculated by adding the digits from left to right, resulting in 136 (1 + 2; 1 + 2 + 3), and then inserting another decimal point: 13.6. After the decimal point, the sequence becomes periodic: 13.666666.

Additionally, to mentally calculate 25 multiplied by 11, one can read off 2 and 5 and position the sum of the decimal points in the middle, resulting in 275. After reading this book, you'll no longer need a calculator. Instead, you'll be able to impress those around you with your lightning-fast mental arithmetic skills.

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