The trick of this multiplication is that you don't have to do anything. By the mathematical identity property, the product of any number multiplied by one is the original number. Therefore, five multiplied by one is five, just as one million multiplied by one is one million.
This method helps to ease the student into the unfamiliar territory of multiplication and uses previously learned addition rules. When any number is multiplied by two, the original number is doubled. Doubling the number is the same as adding the number to itself; therefore the equation "5 x 2" can be rewritten as "5 + 5." With practice, the art of doubling should come easily and naturally.
This method builds upon the trick of multiplying by two. Four is just two doubled, or "2 x 2," which is also "2 + 2." Multiplying a number by four doubles the number twice. Break the equation down so that the number 4 becomes 2 multiplied by 2, so "3 x 4" converts to "3 x 2 x 2." "3 x 2" is essentially "3 + 3," which equals 6, and "6 x 2" is "6 + 6," which equals 12.
This method is a hands-on multiplication trick. Hold your hands up in front of you with your fingers spread. For each number that is multiplied by 9, bend the finger that corresponds to that number. The number of fingers to the left of the bent finger represents the first digit of the answer, and the number of fingers to the right represents the answer's second digit. For example, if 3 is being multiplied by 9, then bend the middle finger on your left hand. The number of fingers to the left is two, and the number of fingers to the right is seven. The answer is 27.
This trick is one of the simplest and works with any number. Add a zero at the end of any number being multiplied by 10. For example, 19 multiplied by 10 is 190, or 19 with a zero added to the end of it. A variation of this method works on numbers multiplied by 100, 1,000 or even 1,000,000. Just add the number of zeros behind the one in the number to the number being multiplied.