Multiplication - one of the four arithmetic operations studied to first grade. In addition to adding it, perhaps, it is most commonly used in everyday life.
This hand does not always have a calculator or a piece of paper.
That's why knowing how to multiply numbers in mind, a must for any modern man.
Moreover, the effectiveness of oral multiplication is achieved by using just a few simple rules and techniques.
You will need
- Knowledge of multiplication tables of numbers from 0 to 9. The ability to add and subtract numbers.
Check whether the problem is described by one of thecases, permitting rapid multiplication. To analyze this, it is not one of the factors of the number 4, 5, 8, 9, 10, 11, 25 or the number formed by multiplying these numbers to powers of 10 (for example, 40, 500, 1000, 250). If so, make a rapid multiplication. When multiplied by the number 10 and its extent, append after the number is multiplied as many zeros as there are in the multiplier, a multiple of ten. This will be the result. For example, 52 * 100 = 5200. When multiplied by 4 double-double the number multiplied. When multiplied by 8 multiplied three times, double the number. When multiplied by 5, multiply the number by 10, then divide by 2. Multiplying by 25, multiply the number by 100, and then double divide by 2. To multiply a number by 9, multiply it by 10 (append one zero) and subtract it is from the result. For example, 56 * 56 * 9 = 10 - 56 = 560 - 56 = 504. To multiply a number by 11, multiply it by 10 and add it to the same result. For example, 56 * 11 * 56 = 10 + 56 = 560 + 56 = 616. If the task does not permit rapid multiplication, go to the next step.
Place the factors in the sequencedescending order of their numbers. To do this, simply compare the length of the factors in the character representation and place on top the longer a factor. For example, you want to multiply 47 to 526. Multiply it will be easier to make if you imagine the task as 526 * 47.
Mentally break each factor on the sum of the numbers up to the order. Imagine the task of multiplication as a product of these amounts. For example, 526 * 47 = (500 + 20 + 6) * (40 + 7).
multiply in mind number. Perform serial numbers multiplying the amount by which the first factor on the amount of the second factor was defeated. After each fold multiplication the resulting number to the previous result. Use simple multiplication rule shown in the first step. For example, 526 * 47 = (500 + 20 + 6) * (40 + 7) = 500 * 40 + 20 * 40 + 6 * 40 + 500 * 7 + 20 * 7 + 6 * 7 = 20000 + 800 + 240 + 3500 + 140 + 42 = 24722.