Multiplication Sheets – 2 Digits x 11

Here is an opportunity to practice your math tricks skills by multiplying 2 digit numbers by 11. Remember – add the two digits in the number being multiplied by 11, then insert the sum in between the two digits. Don’t forget to carry over if it is required.

These multiplication sheets are meant to be solved in your head. One trick is to speak out loud as you solve the problems; this will help you to remember the partial answers better – especially when you have to carry numbers. With just a little practice, you will soon be able to solve these types of problems very quickly.

The answers to these multiplication problems are at the bottom of the page; just scroll down to check your answers.

Squaring Two-Digit Numbers Quickly

Using this math trick, you will be able to square any two digit number very quickly. With a little practice you can do it in your head, or you can do it on paper and still impress others with your math skills. This method of squaring is very easy, and I will be using as an example squaring the number 23.

First, determine the closest number to your number that ends in a zero. In this example, the number is 20. Next, determine the difference between your number and the closest number with the zero. In this case, it will be (23 – 20) = 3. Add the result to your number (23 + 3 = 26). Now, multiply the number with the zero by the sum of your number and the difference you determined:

20 x 26 = 520

Now square the difference you determined before, and add it to the result above:

(3 x 3) + 520 = 529

Presto! There is the square of your number!

Here are some more examples:

The Square of 25

Closest zero number: 20 (note – 30 will also work in this example)

Difference: 25 – 20 = 5

Sum: 25 + 5 = 30

Answer: (5 x 5) + (20 x 30) = 25 + 600 = 625

The Square of 37

Closest zero number: 40

Difference: 37 – 40 = -3

Sum: 37 + -3 = 34

Answer: (-3 x -3) + (40 x 34) = 9 + 1360 = 1369

The Square of 81

Closest zero number: 80

Difference: 81 – 80 = 1

Sum: 81 + 1 = 82

Answer: (1 x 1) + (80 x 82) = 1 + 6400 + 160 = 6561

Noticed how I broke down the (80 x 82) into (80 x 80) + (2 x 80)!

The Square of 12

Closest zero number: 10

Difference: 12 – 10 = 2

Sum: 12 + 2 = 14

Answer: (2 x 2) + (14 x 10) = 4 + 140 = 144

Multiplying by 5, 25, or 125

Multiplying by 5 is just multiplying by 10 and then dividing by 2. Note: To multiply by 10 just add a 0 to the end of the number.

12x5 = (12x10)/2 = 120/2 = 60.

Another example: 64x5 = 640/2 = 320.

And, 4286x5 = 42860/2 = 21430.

To multiply by 25 you multiply by 100 (just add two 0's to the end of the number) then divide by 4, since 100 = 25x4. Note: to divide by 4 your can just divide by 2 twice, since 2x2 = 4.

64x25 = 6400/4 = 3200/2 = 1600.

58x25 = 5800/4 = 2900/2 = 1450.

To multiply by 125, you multipy by 1000 then divide by 8 since 8x125 = 1000. Notice that 8 = 2x2x2. So, to divide by 1000 add three 0's to the number and divide by 2 three times.

32x125 = 32000/8 = 16000/4 = 8000/2 = 4000.

48x125 = 48000/8 = 24000/4 = 12000/2 = 6000.

Multiplying by 9, or 99, or 999

Multiplying by 9 is really multiplying by 10-1.

So, 9x9 is just 9x(10-1) which is 9x10-9 which is 90-9 or 81.

Let's try a harder example: 46x9 = 46x10-46 = 460-46 = 414.

One more example: 68x9 = 680-68 = 612.

To multiply by 99, you multiply by 100-1.

So, 46x99 = 46x(100-1) = 4600-46 = 4554.

Multiplying by 999 is similar to multiplying by 9 and by 99.

38x999 = 38x(1000-1) = 38000-38 = 37962.

Multiplication Trick _ Multiplying by 11

One of the easiest multiplication tricks that I know of is also one of the most impressive. It is the multiplication of two-digit numbers, and, like many othermath tricks, there is an easy rule that you can use to solve problems of this sort very quickly in your head.

An Example:

44 x 11

The technique for quickly solving multiplication problems involving any two-digit number by 11 is easy to remember. Simply add the two digits and insert the result in between the two digit number.

In our example:

44 x 11

4 + 4 = 8, so simply insert “8” between “4” and “4”:

484

So then we have quickly found that
44 x 11 = 484

Birthday Trick

Birthday Trick

Add 18 to your birth month Multiply by 25 Subtract 333 Multiply by 8 Subtract 554 Divide by 2 Add your birth date Multiply by 5 Add 692 Multiply by 20 Add only the last two digits of your birth year Subtract 32940 to get your birthday!

The answer's format is: month/day/year. For example, an answer of 123199 means that you were born on December 31, 1999.

Squaring a 2-digit number ending in 1

• Take a 2-digit number ending in 1.
• Subtract 1 from the number.
• Square the difference.
• Add the difference twice to its square.
• Add 1.

Example:

1. If the number is 61, subtract 1: 61 - 1 = 60.
2. 60 × 60 = 3600 (square the difference).
3. 3600 + 60 + 60 = 3720 (add the difference twice to its square).
4. 3720 + 1 = 3721 (add 1).
5. So 61 × 61 = 3721.

Pretty Cool Huh? Mental math shortcuts can benefit students in elementary, middle, high school and beyond!

Here's another:

1. For 81 × 81, subtract 1: 81 - 1 = 80. 2. 80 × 80 = 6400 (square the difference). 3. 6400 + 80 + 80 = 6560 (add the difference twice to its square). 4. 6560 + 1 = 6561 (add 1) 5. So 81 × 81 = 6561.