How to Calculate Math Quickly

You may think that people who excel in mathematics are more intelligent. The truth is that they use strategies and methods that enable them to make speedy mental calculations. Anyone can learn to calculate math quickly by knowing a few rules and tricks.

Difficulty: Moderately Easy

Instructions

1. Find the sum of all even numbers from 2 to a selected even number by first dividing the selected number by 2 and then multiplying this result by the next number. As an example, use 10 as the selected even number and divide it by 2 to get 5 as a result. Now multiply 5 by 6 which is the next number after 5. So 5 X 6= 30 is the sum of all even numbers from 2 to 10.

2. Subtract a large number for 1,000 by using this basic rule. Subtract all numbers from 9 except the last one which you then subtract from 10. Apply this rule to 1000-758 to get 9-7=2, 9-5=4 and 10-8=2. The final answer is 242.

3. Learn to use the 11 rule to multiply two digit numbers. Multiply 53 X 11 by taking 53 and placing a space between the first and last digits 5 and 3 i.e. 5_3 then add 5 and 3 to get 8. Place 8 in the space to get 583. If the number in the middle adds up to a two digit number then use the digit in the ones place for the space and add 1 to the first number.

4. Multiply a large number by 5 with this easy trick. Take the large number and divide it by 2. If the result is a whole number add zero at the end but if there is a remainder than add 5 at the end. As an example, multiple 3,485 X 5 using this trick. First divide 3,485 by 2 and you get the result 1742 with a remainder of 1. Using the rule, 17,425 is the answer to the multiplication.

5. Divide a large number by 5 by first multiplying the large number by 2 and then moving the decimal point one place to the left of the last digit. Let's divide 89,221 by 5 using this technique. Multiply 89,221 by 2 to get 178,442, then placing the decimal point to the left of 2 you have 17844.2 as the answer to the division.

6. Know how to square numbers that end in 5 by using this technique. Multiply the first digit by itself and add 1 and then place 25 at the end of this result. Use 75 X 75 to demonstrate this technique. Multiply (7) X (7+1) =56, then add 25 to this result and get 5,625. Check the result by squaring 75.

7. Estimate percents of any number by using specific rules to calculate the math quickly (see the Resources). Figure out a 15 percent tip of 53.55 by first rounding this to the nearest whole number 54, and then multiplying by 3 to get 162. Now divide this result by 2 and get 81. Place a decimal point one place to the left of 1. The answer is 8.10.

Resources

• Get information here on percent calculations.

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[andydfrain]

on 6/6/2008 the english you have in step 6 is misleading thank goodness you inlcude the scientific notation. I am not complaining, but rather bringing it up so you might fix it you say "Multiply the first digit by itself and add 1 and then place 25 at the end of this result." what you want to say is Multiply the first digit by itself after first adding 1 to it, and then place 25 at the end of this result. or you can say Multiply the first digit by the sum of itself and, and then place 25 at the end of this result. The second version of my suggested corrections might be more proper but I prefer the first version because it is more plain spoken. any just thought you might want to make that correction. it messed with my head for second till I looked at the equation. but most looking at this page are less likely to be as at ease with numbers as I am. I was looking for computational tips