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Fast mental multiplication methods enable you to check whether the cashier asks for the right amount during checkout.

Anyone taking the SAT test is short on time. Being able to multiply fast mentally allows you to answer more questions, thus score higher and get accepted in that Ivy League college you’re dreaming about.

Many people are outright terrified having to do math in their head. They need to reach for the calculator. Surprisingly and thankfully, there exists a number of fast mental multiplication methods. In this article, TutorZ presents 5 of them.

Method #1 – Multiplication by 4
Most people need to find the calculator first in order to multiply 58 by 4 which is 232.  But there is an easy way to compute the result in one’s head (although for some of you this technique might be obvious).

Steps for method #1 – Multiplication by 4

Example:    58 x 4

1. Step 1 – 58 x 4 = (58 x 2) + (58 x 2)
2. Step 2 – (116) + (116) = 232

The result is 232. That wasn’t so hard, was it?

 
Method #2 – Multiplication by 5
Many people memorize the multiplication table for 5 with smaller numbers quite easily. For example; 5 x 1 = 5, 5 x 2 = 10, 5 x 3 = 15 and so on. But when dealing with large numbers, it gets complicated. Or do you know 2681 x 5 by heart? If not, I suggest the following simple technique to multiply by 5.

Steps for method #2 – Multiplication by 5:

1. Step 1 – Take the larger number and divide it by 2 (in other words half it).
2. Step 2 – If the result of step 1 is a whole number (no trailing .5) append a 0.
3. Step 3 – If the result of step 1 is a fraction (that is .5 at the end) forget the fractional part. Instead append a 5 at the end of the result.

First Example:  12 x 5

1. Step 1 – 12 / 2 = 6.
2. Step 2 – The result of step 1 is a whole number (6), so we append a zero to the six.
3. Step 3 – Not applicable because no fraction is involved.

The result is 60.

Second Example:   2681 x 5

1. Step 1 – 2681 / 2 = 1340.5
2. Step 2 – Not applicable because the result of step 1 is a fraction.
3. Step 3 – The result of step 1 is a fraction (1340.5), so we ditch the .5 in favor of the 5 at the end.

The result is 13405.  Amazing!
 

Method #3 – Multiplication by 11
We all know that when multiplying by 10 you simply add 0 to the end of the number. But multiplying by 11 is not that simple. Or is it?

These are 4 simple steps to multiply a two-digit number by 11.

1. Step 1 – Take the number other than 11 and imagine a space between two characters (in this example, we use the number 52).
2. Step 2 – Now in the space in the middle copy the numbers.
3. Step 3 – Add the inner two numbers.
4. Step 4 – Write the result of step 3 down in the middle.

First Example:   52 x 11

1. Step 1 – 5_2
2. Step 2 – 5_5_2_2
3. Step 3 – 5_(5+2)_2
4. Step 4 – 5_(7)_2

The result is 572.

Second Example:   99 x 11

If adding the numbers in parentheses obtained a two-digit number, as 18 is in this example, remember the second number and add one to the first number:

1. Step 1 – 9_9
2. Step 2 – 9_9_9_9
3. Step 3 – 9_(9+9)_9 = 9_18_9
4. Step 4 – (9+1)_8_9 = 10_8_9

The result is 1089.
 

Method #4: Multiplying by Itself (Squaring)
This technique quickly squares a number that ends in 5. A number that ends in 1,2,3,4 or 6,7,8,9 does not apply to method #4. This is how it goes:

1. Step 1 – Take the first digit off of one of the numbers.
2. Step 2 – Add one to this first digit.
3. Step 3 – Multiply the result on the first digit, the same first digit as in step 1.
4. Step 4 – Append 25 at the end.

Example:     25 x 25

1. Step 1 – 2
2. Step 2 – 2+1 = 3
3. Step 3 – 3 x 2 = 6
4. Step 4 – 6 append 25 = 625

The result is 625.

For those who what to solve method 4 even quicker, note it can be written in a single line:  (2+1) x 2 append “25” = 625.
 

Method #5: Complex Multiplication
Unless you’re the savant Daniel Tammet who effortlessly multiplies large numbers we need to use a calculator.  Fortunately, if one of the numbers is even, you can successively multiply one number by 2 and divide the other by 2 also.

Example:     32 x 125

1. Step 1 – 16 x 250 is the same as
2. Step 2 – 8 x 500 is the same as
3. Step 3 – 4 x 1000 which you can now easily solve as 4000.

Thus, the result is 4000.

These five fast mental multiplication methods empower you to double check the amount you have to pay at the cash register, or if the situation is right to impress your math teacher, parent or even your boyfriend or girlfriend.

Still having trouble getting these techinques? Then we recommend you to get in touch with one of TutorZ’ math whizz tutors to learn these or other five fast mental multiplication methods.

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