To read, multiply and divide in mind large numbers not so difficult as it seems at first sight. There are several methods allowing to make quickly and easily such calculations.
Instruction
1. People developed a set of the receptions allowing to calculate large numbers in mind. To multiply, divide, square, not obligatory to use the calculator or a writing-book sheet at all. To make difficult calculations in mind, it is enough to remember a number of simple rules.
2. To increase two-digit number by 11, it is necessary to put its first and second figure and to deliver it in the middle of number. For example, it is required to increase by the 11th 27. Put 2 and 7 and place the turned-out nine in the middle of number. 297 will turn out. If the sum of the first and second figures gives two-digit number, it is necessary to insert in the middle only its second figure, and to the first figure of initial number - to add unit. For example, we multiply 11 by 49. The sum 4 and 9 is 13. We place the three between the four and the nine, 439 turn out. Then we add unit to the four - we receive 539.
3. To square the number which is coming to an end on 5 it is necessary to increase the first figure by itself plus unit, and then to add at the end 25. For example, the square 95 is equal 9*(9+1)_25 = 9*10_25 = 9025.
4. It is easy to multiply large numbers by 5 too. At first look whether the number completely is divided into 2. If shares, then the result of its division on 2 at the end of which zero is written down will be result of its multiplication on 5. For example, 620*5 = 310_0 = 3100. If the number is not divided into 2 without the rest, reject the rest and add instead of zero the five at the end. For example, 621*5 = 310_5 = 3105.
5. To increase two-digit number by 4, it is enough to increase of it by 2 twice. For example, 43*4 = 43*2*2 = 86*2 = 172.
6. To multiply one large number on another, look whether one of them is divided into two without the rest. If shares, it is possible to apply a method of simplification of multipliers to multiplication, consistently dividing into 2 one multiplier and multiplying by 2 second multiplier. For example, 32*105 = 16*210 = 8*420 = 4*840 = 3360.
7. It is better to put large numbers in mind, at first having divided one of them into parts. For example, 3570+5780 = (3000+5000) + (570+780) = 8000+(500+700)+70+80 = 9200+70+80 = 9350. The same reception can be used and at subtraction, consistently segmenting the numbers more convenient for calculation.
8. To subtract number from 1000, break it into the making figures and subtract each of them of the nine. Subtract the last figure not from the nine, and from ten. For example, 1000-523 = (9-5) _ (9-2) _ (10-3) = 477.
9. To divide a large number into 5, increase it in mind by two and divide into ten. For example, 182/5 = (182*2)/10 = 364/10 = 36.4.