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# How quickly to increase in mind two-digit number on 11? The entertaining mathematics of

arises At once a question and why to us actually it is necessary? Agree, knowledge never happens superfluous and unnecessary. Perhaps, you need to solve quickly a mathematical problem at the Olympic Games where it is not allowed to use the calculator. And it is possible, you want to entertain children or to surprise someone. Irrespective of your purposes and tasks, it is very simple to make it.

It is really very simple! Takes not enough time, and makes indelible impression on the interlocutor not familiar with a similar mathematical trick.

So, suggest the interlocutor to increase any two-place number on 11. And to make it in mind. While it multiplies numbers, calculate the answer (a method lower). If the answer of the interlocutor true, praise the genius of mathematics and tell that you made it quicker. If the answer wrong, and the person refuses to believe that it is possible to multiply these numbers in mind, overpersuade him.

And all is very simple. That any two-digit number to increase

on 11, it is necessary to put its first and last figure and figure - to enter result in the middle of two-place number.

Examples: we Write

32x11

“3_2“

3+2=5 Are put. And now instead of a gap enter the received result.

54õ11

we Write “5_4“

5+4=9 Are put. And now instead of a gap enter the received result.

Still you do not trust? Use the calculator!

If at addition of two numbers we receive two-place number, we arrive a little in a different way.

Example: we Write

57õ11

“5_7“

5+7=12 Are put. We add unit to the five, and we write the two to the middle.

As you can see, mathematics it not only dry figures, statistics and drudgery. There is also surprising “an entertaining mathematics“ .

The entertaining mathematics is a pleasant entertainment for all times, and in any society. It conducts the history with the 20th century B.C.! Yes, in ancient papyruses entertaining tasks which are included also in modern collections are found. Mathematicians of all times - Diophantus Aleksandriysky, Leonardo Pizanscy (Fibonacci), Niccolo Tartaglija was fond of the composition of such tasks...

The collections of mathematical entertainments reminding modern began to appear from 17th century. The most popular collection of mathematical problems of that time “The pleasant and entertaining tasks considered in numbers“ was made by the mathematician and the poet Claude Gaspard Bachet de Meziriac. At the same time “Mathematical and physical entertainments“ of the French mathematician and writer Jacques Ozanam enjoyed popularity.

Classical became four-volume work on entertaining mathematics, the big contribution to entertaining mathematics created by the French mathematician Eduard of Luke in the 19th century

At a boundary of the 19th and 20th centuries was made by ingenious inventors of games and puzzles the American chess player Samuel Lloyd and Englishman Henry E. Dyyudeni. to

the Entertaining mathematics of the second half of the 20th century is presented by a series of the remarkable books belonging to a feather of the famous American popular writer of mathematics Martin Gardner.

Now it is possible to find the whole websites devoted to mathematical puzzles in the Internet. And for our generation “Mathematical sharpness“ of B. A. Kordemsky, “In a sharpness kingdom“ E. I. Ignatyeva and of course, remarkable books of Ya. I were desktop. Perelman “Live mathematics“, “Entertaining arithmetics“, “Entertaining algebra“ and “Entertaining geometry“. Open them for yourself and you, and it is never not necessary to miss any more!