What is the easy way to square a number ending with 5?

To raise (in memory) to the square of the number of completed number "5", perform the following operations: The final result of the first digit, it will be "25"; 2 The initial numbers calculated by multiplying the number formed from the initial digits (no final Fridays) alleged the square of the number by the number one greater. More specifically explain examples: 35 ^2 = 1225 (because 3 *4 = 12 and tip 25) 75 ^2 = 5625 (because 7 * 8 = 56 and tip 25) 105 ^2 = 11025 (because 10 *11 = 110, and the tip 25)

Arabic numerals, actually digits Indian europeizowane - numbers currently used widely around the world to write numbers. Those are the signs 0,1,2,3,4,5, 6,7,8 and 9, and initially were used to represent numbers in the decimal system. Now also used in other systems (for example, the hexadecimal digits greater than 9 are symbolized with successive letters of the Latin alphabet). Numbers and decimal positional system originated in India, which about the seventh century the Arabs invaded. Their prey (except treasures, works of art and utility products, sometimes very valuable) died too ancient Indian writings including those containing knowledge of mathematics and astronomy. Arab scholars with knowledge of Sanskrit had access to this knowledge. Digits entered into common use and their promoter was a Persian mathematician Muhammad ibn Musa al-Chuwarizmi, who applied them to the study of algebra and trigonometry. The digits to the West in the Middle Ages, the Arabs spread (hence their name received in Europe), and their promoter in Europe was the Italian mathematician Fibonacci. As a curiosity should be mentioned that nowadays used in Arab countries digits differ significantly from traditional ones, adapted to the Latin alphabet and Arabic numerals today are, in turn, signs: . Figures with those digits are stored in the same way as in our system - that is to the right of unity.

the number in question is X5, X is any number (1 or2 or3 or4 or......).

• (X5)^2 = X*(X+1) and the you put25 at the end
• if X is one then the number is15^2 and,1*(1+1) which is2, then put25 and the number is225
• if X is two then,2*(2+1)=6,the answer is625
• if X is three then,3*(3+1) =12, the answer is1225
• If X is four then,4*(4+1) =20,the answer is2025