Oral account in the school Rachinsky
 

N. P. Bogdanov - Belsky "Oral account in the school Rachinsky".

Cyril Syzran in the old brains coached, and now all on the calculator consider.

Keyword - brains.

730:365=2
But the intermediate results were recorded on paper... :(

Many years in school could not memorize the multiplication tables, so getting out of the situation instantly folding in mind...I'm still not firmly remember...was full DiBella that gave me a great opportunity brilliantly to take the examination on the Mat.Sciences in the best University of the evil Empire...So me solve this example is extremely simple in mind and was in 9 years, and now even more so...

Will complicate the task itself, identifying 10 for X!!!...We are automatically in the mind will solve the problem more complicated: 50x50+h+h+h+h+h Here X=50...And you can take, for example X=1000000001...and I have in mind will give You, without batting an eye, the answer earlier than You would rape his wretched calculator...:D

Have(I do this in the mind), but explain to others, who know the multiplication table...

X squared + (X+1)squared+etc....Knowing the well-known formula , which is easy to derive in the mind (X+Y)x(X+Y)=Xxx+HHO+Ear...in the numerator of the y is equal to 1, then 2, 3 and 4...Disclose the sums of squares...

Have numerators 5 X squared plus double works X take out the brackets: 5xxx+ 2(1+2+3+4) + 1x1+2x2+3x3+4x4=5xxx+20xx+30...replacing X, 10: HH+20x10+30=730...If X=50, we have h+20x50+30=12500+1030=13530...

In a German school teacher gave the children of other problems for Example..., 1+2+3+...+498+499=? One student immediately, in my mind, gave the answer...Apparently he was too lazy to fold, as did all...Later in the story he came as the great mathematician, opening for science formula for the sum of arithmetic progression in childhood...It's one of the few times in history when the Prodigy have not lost their opportunities in adulthood...

Forgot to say, the mathematician Gauss was...

Everything is simple! Bit permutations and turns
(1+499)+(2+498)+(3+497)+ so on

Agree...Specially so graphically on figures set a task that everyone can feel like a Gaussian...:)

If I have a task to annoy your opponent, then I suggest him to play...He's using the calculator, and I mind much faster and without errors add up, subtract, multiply, divide, erected in the squares and remove the roots with six-digit numbers(up to a million !!!)...With particular cynicism this experiment I spend on the individuals of the fair sex...it directly produces stunning effect...They are so objaut after smart genius(that is me)...But can any fifth grader with 5 mathematics to teach such "art", but anyone naturally about this don't say...:D