# What's the Algorithm Behind This Easy Mental Multiplication Trick?

• abdo375
In summary, the trick is to use the inverse of the square root of the number you are trying to multiply.
Basically, because of where the tens and the ones intersect, you get one corner as the hundreds (ten*ten), two corners are tens (1*10, 10*1), and one corner is the singles (1*1)

I only watched the first example, obviously you could expand it to hundreds and thousands and such

That's kind of neat.

Very nice, I will have to show that to my younger siblings. Thanks for sharing the link.

(10 + 2)(20 + 1)
10 * 20 + 10 * 1 + 2 * 20 * 2 * 1
Doing the trick does the same thing as multiplying that out the way you would with variables in there. (you know, like if it
were (x + 1)(x - 5) or something and you wanted to expand it)

EDIT: That is if this is the trick I'm thinking of.

Last edited:
moose, that's basically what it does

If this method helps you, then go for it. However, it has its limitations. Try this one the traditional way and the graphical way:

999 X 999

It's an interesting way to multiply numbers, but equivalent to just summing the product of all the digit pairs. Frankly, drawing the picture is just slowing him down. Very creative though, don't think I would have thought of doing it.

Hey, we should come up with other ways to do math using pictures.

I like the trick that you can use to square numbers. Let's say you want to square 28... You know that 30*30 = 900.

If you then use the derivative of x^2 to approximate it, you subtract 2*30*(30-28), resulting in 780. Then as a correction, you add in the change squared (30-28)^2, so your answer is 784. This is really simple around 50, because you just subtract or add 100s.

So if you want to find x^2, and know y^2
x^2 = y^2 - 2y(y - x) + (y - x)^2

Really fast and easy to do. I would think that most people on this board already know of this "trick" though.

Wow, that's pretty neat.

Here is an even neater trick!

http://www.shiar.org/ticalcs/ticlxpix/ti83+01.gif

## 1. What is the "Easy Mental Multiplication Trick"?

The "Easy Mental Multiplication Trick" is a method for quickly and accurately multiplying two numbers in your head without the use of a calculator or pen and paper. It involves breaking down the numbers into smaller, easier to multiply parts and then combining the results.

## 2. How does the "Easy Mental Multiplication Trick" work?

The trick involves breaking down the numbers into their tens and ones digit, and then multiplying these smaller parts. The results are then combined to get the final answer. For example, to multiply 24 and 13, you would break them down into 20 and 4, and 10 and 3, and then multiply 20 by 10, 20 by 3, 4 by 10, and 4 by 3, and add the results together to get 312.

## 3. Can anyone learn the "Easy Mental Multiplication Trick"?

Yes, the "Easy Mental Multiplication Trick" is a simple and straightforward method that can be learned by anyone. It just requires some practice and familiarity with basic multiplication tables.

## 4. How can the "Easy Mental Multiplication Trick" be useful?

The "Easy Mental Multiplication Trick" can be useful in situations where a calculator or pen and paper are not readily available, or when there is a need for quick mental calculations. It can also help with building mental math skills and increasing overall calculation speed.

## 5. Are there any limitations to the "Easy Mental Multiplication Trick"?

The "Easy Mental Multiplication Trick" may not be suitable for very large numbers or complex calculations. It is best used for multiplying two-digit numbers or numbers with simple multiples of 10. It also requires some practice and may not be suitable for those who struggle with basic multiplication concepts.

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