## TIP 6: Multiply a number by 9

In this case just add a zero to the end of the number and subtract it from the beginning number. Let's do the following multiplication: 44 x 9.

Adding a zero to the end of number 44 gives us 440.

Then we subtract from this value the initial value: 440-44 = 396.

So 44 x 9 = 396.

Another examples:

27 x 9 = 270-27 = 243.

56 x 9 = 560-56 = 504.

33 x 9 = 330-33 = 297.

## TIP 7: Multiply a number by 99

In this case just add 2 zeros to the end of the number and subtract it from the beginning number. Let's do the following multiplication: 44 x 99.

Adding 2 zeros at the end of number 44 gives us 4400.

Then we subtract from this value the initial value: 4400-44 = 4356.

Therefore 44 x 99 = 4356.

Another examples:

27x99 = 2700-27 = 2673

56x99 = 5600-56 = 5544

33x99 = 3300-33 = 3267

## TIP 8: Multiply a number by 101

When a 2-digit number **AB** multiplied by 101, the result will be **ABAB**. Some examples:

43 x 101 = 4343

32x101 = 3232

14 x 101 = 1414

## TIP 9: Multiply 2 numbers (2 digits) that have the same number as the tens, and the sum of their unit digits is 10

Examples of multiplications that can be done with this method: 42x48, 53x57, 21x29, 35x35, 87x83, 94x96, etc.

The following steps must be followed:**1)** We multiply the digit of tens (which is equal to the 2 numbers) by the number following it;**2)** We multiply unit numbers normally;**3)** We put the two parts together.

Let's do the following multiplication: 53 x 57:

Step **1**:

5x6 = 30

Step **2**:

3x7 = 21

Step **3**:

We put the two numbers together: **3021**.

So 53 x 57 = 3021. Bearded!

Another example: 94x96:

Step **1**:

9x10 = 90

Step **2**:

4x6 = 24

Step **3**:

We put the two numbers together: **9024**.

So 94 x 96 = 9024. Bearded!

## TIP 10: Sum of n first odd natural numbers

The sum of **no** first odd natural numbers equals **no ^{2}**. Examples:

1) Sum of the first 5 odd natural numbers (1 + 3 + 5 + 7 + 9):

The sum is equal to 5^{2} = 25.

2) Sum of the first 15 odd natural numbers:

The sum is equal to 15^{2} = 225.

## TIP 11: Multiply a number by 15

Add the number with its half, and multiply the result by 10.

Examples:

14×15 =(14+7)×10=210

10,4×15=(10,4+5,2)×10=15,6×10=156