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To "cast out nines" from a single number, its decimal digits can be simply added together to obtain its so-called digit sum. The digit sum of 2946, for example is 2 + 9 + 4 + 6 = 21. The digit sum of 2946, for example is 2 + 9 + 4 + 6 = 21.
Mental calculation often involves the use of specific techniques devised for specific types of problems. People with unusually high ability to perform mental calculations are called mental calculators or lightning calculators. Many of these techniques take advantage of or rely on the decimal numeral system.
The Trachtenberg Speed System of Basic Mathematics by Jakow Trachtenberg, A. Cutler (Translator), R. McShane (Translator), was published by Doubleday and Company, Inc. Garden City, New York in 1960. [1] The book contains specific algebraic explanations for each of the above operations. Most of the information in this article is from the ...
Casting out nines is a quick way of testing the calculations of sums, differences, products, and quotients of integers in decimal, a method known as long ago as the 12th century. [ 3 ] 9 is the only square number that is the sum of two consecutive, positive cubes: 3 2 = 9 = 1 3 + 2 3 {\displaystyle 3^{2}=9=1^{3}+2^{3}} [ 4 ]
It turns out functions like this have certain properties that cast insight into math topics like Algebra and Number Theory. British mathematicians Bryan Birch and Peter Swinnerton-Dyer developed ...
Rule of nines or rule of nine may refer to: Rule of nine (linguistics), an orthographic rule of the Ukrainian language. Rule of nines (mathematics), a test for divisibility by 9 involving summing the decimal digits of a number; Wallace rule of nines, used to determine the percentage of total body surface area affected when assessing burn injuries
RELATED: Hard Math Problems That’ll Test Your Smarts. Safe code 1. Math puzzle. To open this safe, you have to replace the question marks with the correct figures. You can find this figure by ...
For divisibility by 9, this test is called the rule of nines and is the basis of the casting out nines technique for checking calculations. Digit sums are also a common ingredient in checksum algorithms to check the arithmetic operations of early computers. [ 3 ]