# 암산천재의 비밀. 8분후 당신도 암산 천재가 될 수 있다!! You can be a mental calculation Master in 8minutes.

You can be a mental calculation Master in 8minutes.
Stay focused and be with me.
Hi! This is [susinsaem] in Korea. I’m a professional math teacher in Kangnam, South Korea.
Today, I have come up with a great tip that tells u how to do a real quick mental calculation.
We are not doing a complicated multiplies like 64 by 86 today,
but i'm going to start with easy ones like multiplying 12 by 13.
I guess most of you would multiply 2 by 3, 1 by 3, but it’s not the way I am going to tell you today.
I think almost every one of you knows the multiple tables from 1 to 9.
And I heard some Indian students learn the multiple tables from 1 to 19,
but I believe you don’t want to waste your time to memorize the multiple tables from 1 to 19 all over again just to make a quick calculation.
Today I would start calculating with the easy numbers that you sometimes meet in your actual life. This is a real great and easy hint.
In Korean we say “honey tip” which means that real sweet tip.
Please practice number of times to get used to it.
It can reduce your calculating time 5seconds to 2or 3.
If you are used to it you can get even the answer in one second.
If you are a student and used to it, I’m sure you are not going to say “I did’t have enough time to solve all the problems” for your excuses in your math exam.
The main purpose of doing a quick mental calculation is to save your time of seconds which will take your math skills higher level.
Okay Let’s start.
I think, in this multiplication most of you would start with multiplying 2 by 3,
that’s 6. And 1 by 3, that’s 3and 12 by 1. And you come up with 156 for the final answer.
From now on, never do this way again.
Just multiply 2 by 3, that’s 6 and get the sum of 2 and 3, that’s 5.
There is 1 at the 2nd digit so you get 156.
Just multiply 2 by 3, that’s 6
and get the sum of 2 and 3, that’s 5.
There is 1 at the 2nd digit so you get 156.
Let’s change numbers.
Multiply 14 by 12.
Let’s do it quickly.
Multiply 4 by 2 that’s 8
and add 4 and 2, that’s 6. You get 168.
Do you understand?
You are getting it right?
Multiply 4 by 2 that’s 8
and add 4 and 2, that’s 6. You get 168
Okay now I’m going to change numbers again.
Multiply 15 by 14.
In here according to my way, multiple of 5 by 4 is 20.
All you have to do is put “2” to the next digit. Mark 2.
And add the numbers again. That’s 9.
And the “9” and “2” that we marked add again.
Then the final answer will be 210.
Let’s solve another one.
Multiply 17 by 13.
7 by 3 is 21.
Write 2 down.
And now what?
Add 7 and 3 again. That’s 10.
1 has to go to the next digit.
. For those who don’t understand, I’m going again.
7 by 3 is 21.
and 1 by 3
that’s 51, and 17 here.
That’s 221, right?
But we are trying not to calculate that long way.
7 by 3 is 21.
And sum of 7 and 3 is 10.
“1” went to the next digit.
It’s about to be 100 but 100 becomes 200 with the addition of next digit number.
Let’s go once again.
What is multiple of 17 by 18?
It seems complicated but it’s easy.
. 7 by 8 is 56.
And for the addition? It’s 15.
There are two “1” went to the next digit.
Therefore it’s 306.
If you don’t understand, I’m sorry I can’t help it.
.One more, 37 by 33.
. This is very good tip when the numbers have same second digit numbers, and the addition of first digit is 10
Stay focused.
7 by 3 is 21
and what is sum of 7 and 3?
It’s 10 right?
Then 10 goes to the next digit.
In this case with the “1” that came up from first digit,
3 becomes 4.
And now multiply 4 by 3.
It’s 12. So the answer is 1221.
May be you want to say “Oh uh… come again?” or “ don’t get it” Listen carefully.
. IF SECOND DIGIT NUMBERS ARE SAME, AND THE SUM OF FIRST DIGIT IS 10,
FIRST MULTIPLY 7 BY 3
AND “1” GOES TO THE NEXT DIGIT AND BECOMES 4.
AND FINALLY MULTIPLY SECOND DIGIT NUMBERS. So it’s 1221.
With this Theory, let’s try different numbers.
. 13 by 17
3 by 7 is 21.
1 goes to the next digit.
2 by 1 is 2. It’s over 221.
One more! 16 by 14.
6 by 4 is 24.
. And again 1 goes to the next digit.
2 by 1 is 2.
One more! 55 by 55.
These numbers have same second digit numbers, and sum of first digit is 10.
5 by 5 is 25
Again “1” goes to the second digit. 6 by 5 30.
Therefore 55 by 55 is 3025.
Let’s try this one.
What is multiple of 72 by 78?
2by 8 is 16
and 8 by 7 is 56.