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# Top 7 Mental Math Tricks Work out your brain and check out some cool math tricks that will make calculations faster and simpler! Try the trick by doing the “now you try” section, and keep track of your answers to compare it to the solutions at the end.

## 1. Subtracting from 1000

Use this trick when subtracting any number from 1000. To do it, just subtract every number except the last number (place value of one) from 9. Then subtract the last number from 10.

For example: 1000 – 682 = ?

Step 1: 9 – 6 = 3

Step 2: 9 – 8 = 1

Step 3: 10 – 2 = 8

Now you try: What is 1000 – 924?

## 2. Multiplying by 11

When multiplying a two digit number by 11, first put a space between the two numbers. Then, add up the two numbers and put the answer in the middle. That number makes up the overall answer to the multiplication.

Example: 11 x 42 = ?

Step 1: 4_2

Step 2: 4 _(4+2)_ 2

Step 3: 462

Now you try: What is 11 x 27?

## 3. Dividing by 10 or 100

When dividing a number by 10, add a decimal at the end of that number, and move the decimal place one spot to the left of that number. It is the same concept when dividing a number by 100, but instead of one spot, move the decimal place two spots to the left of that number.

Example: 3489 ÷ 10

Step 1: 3489

Step 2: 348.9

What if you were to do 3489 ÷ 100

Step 1: 3489.

Step 2: 34.89

Now you try: What is 5692 ÷ 10? What is 5692 ÷ 100?

## 4. Multiplying by 10 or 100

To multiply by 10, do the opposite of what we did when dividing. Move the decimal place one spot to the right of that number. If there is no number when you move the decimal point, and/or if there is no number to the left of that decimal point, add zero in the space. To multiply by 100, move the decimal palace two spots to the right of that number.

Example: 679.2 x 10 = ?

Step 1: 6792.

What if there is no number to the left of the decimal point after moving it?

Example: 679.2 x 100 = ?

Step 1: 6792_.

Step 2: 67920.

Now you try: What is 54.7 x 10? What is 54.7 x 100?

## 5. Squaring numbers that end with 5

To square numbers that end with 5, remove the ending 5, and take the remaining numbers, and add 1 to them. Then multiply the result with the remaining numbers. Take that answer and add 25 to the end to get the final answer.

Example: 752 = ?

Step 1: 7 + 1 = 8

Step 2: 8 x 7 =56

Step 3: 5625

Now you try: What is 852?

## 6. Multiplying numbers that end with 0

When multiplying two numbers that end with 0, remove the zeros, and add multiply the two numbers without the 0. Then count the total number of zeros that were in the original equation, and add them to the answer.

Example: 500 x 30 = ?

Step 1: 5 x 3 = 15

Step 2: There are 3 zeros

Step 3: 15000

Now you try: What is 6000 x 800?

## 7. Multiplying by 9

When multiplying a number by 9, multiply the number by 10 first, and then subtract the original number from the result.

Example: 59 x 9 = ?

Step 1: 59 x 10 = 590

Step 2: 590 – 59 = 531

Now you try: What is 24 x 9?

## Solutions

1. 1000 – 924 = 76
2. 11 x 27 = 297
3. a) 5692 ÷ 10 = 569.2
b) 5692 ÷ 100 = 56.92
4. a) 54.7 x 10 = 547
b) 54.7 x 100 = 5,470
5. 852 = 7,225
6. 6000 x 800 = 4,800, 000
7. 24 x 9 = 216

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