Math Tricks for Elementary Students
Addition and Subtraction
- Adding and subtracting large numbers in your head becomes easier when you break numbers down in to manageable parts. For example, to find 78 + 57, break the numbers down in to 70 + 8 and 50 + 7. Add 70 and 50 to get 120, then add 8 and 7 to get 15. Adding 120 + 15 gives you the answer of 135. The same concept applies to subtraction problems as well.
Multiplication and Division
- Many tricks exist to help students memorize multiplication and division tables. Examples include checking the last digit of a number to see if it is even. If so, it is divisible by 2. The nine times table often proves difficult for students to master. Show students the pattern in the answers to help them. Starting with 9, the next answer has a 1 in the 10s place and an 8 in the ones place. This pattern continues, with the next answer having a 2 in the 10s place and a 7 in the ones place. Another trick for multiplying by nine is to use your fingers to find the answer. If the problem is 7 x 9, hold all your fingers in front of you and count over seven fingers, beginning with the thumb on your left hand. Putting the seventh finger down leaves you with six fingers separated from three other fingers, or 63, the answer to your problem.
- Teach elementary students to find 10 percent of a number and then use this information to multiply and find any percentage ending in 0. For example, 10 percent of 90 is 9. Find 40 percent of 90 by figuring 9 x 4, which is 36. Take this concept one step further and find any percentage ending in a 5, as well. Simply take half of 10 percent to find five percent, then add this amount to your other answer. For example, to find 45 percent of 90, you find 40 percent as described above, which is 36. You then find five percent by taking half of 9, which is 4.5. Add 36 + 4.5 to find 40.5 which is 45 percent of 90.
- Rounding helps students check the appropriateness of answers. In this way, they can check homework and tests, easily catching mistakes. For example, if they are adding two numbers in the thousands, by rounding each number and checking the answer and theirs, it becomes obvious whether they might have a wrong answer.