How to do 1565 x 1197 in 10 seconds without a calculator and paper?

In summary, Jekertee is willing to teach us the method of doing this in 10 seconds without a calculator and scratch paper.
  • #1
Jekertee
43
0
How to do this in 10 seconds without a calculator and scratch paper?

1565 x 1197 = ?
 
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  • #2
Call it 1565 * 1200 which is just (1565 * 2 *100) + 1565*1000
The subtract 1565 three times.
 
  • #3
Do you know how to apply Indian's classic calculation method to this ?
 
  • #4
Sorry never heard of it.
 
  • #5
Jekertee said:
How to do this in 10 seconds without a calculator and scratch paper?

1565 x 1197 = ?

Ask google - it takes less than 5 seconds!
:))
 
  • #6
I don't think that'll work.
 
  • #7
I googled 1565 x 1197, and got the answer: 1 873 305.
It didn't take 10 seconds. Then I googled "India's classic calculation method" but I got nothing I could use.

Jekertee, are you willing to teach us the method?
 
Last edited:
  • #8
Here's a question: how randomly chosen is that pair of numbers? After you demonstrate the method, I want to see you do the same thing with numbers provided by an audience member.
 
  • #9
jimmysnyder said:
...
Jekertee, are you willing to teach us the method?

:shy , Jim, I din't know that method also, I made a quizz thinking that someone knew to tell me too

I input random numbers into the search box of google but found only strange result. It's amazing to me the example I gave works on your search
 
  • #10
Jekertee said:
...I input random numbers into the search box of google but found only strange result.

Only numbers? Didn't you specify an operator?

What about an expression like (into the search box):
2*17.9 + 3**3

:smile:
 
  • #11
Jekertee said:
I din't know that method also, I made a quizz thinking that someone knew to tell me too
Is there any information you could give us to help search for it?
 
  • #12
1565 x 1200 - (1565 x 3) = ?

4 x 1565 = 6000 + 240 + 20 = 6260
6260 x 300 - (1565 x 3) = ?
6260 x 3 = 18000 + 600 + 180 = 18780
18780 x 100 = 1878000 - (1565 x 3)
1565 x 3 = 4500 + 180 + 15 = 4695
1878000 - 4695 = ?
=1873305

This is one way, and it's probably not the fastest, but it uses an ancient technique of multiplying where one number was halved, and the other was doubled. Or multiplied by 3, and divided by 3.
 
  • #13
it's called vedic math. if you google it, you'll find a ton of sites with math tricks here and there. but usually, they don't involve numbers that big.
for example:
when multiplying 2, 2-digit numbers with the same tens digits and two ones digits that add up to 10, (ex. 23 x 27 ) the vedic stuff is useful.
you just multiply the tens digit by the next number up, so multiply 2 by 3 and get 6.
then multiply the two ones digits, and get 21.
the answer is 621.

there's tons of little things like that that you can find on google.
 
  • #14
nabeelr said:
when multiplying 2, 2-digit numbers with the same tens digits and two ones digits that add up to 10, (ex. 23 x 27 ) the vedic stuff is useful.
you just multiply the tens digit by the next number up, so multiply 2 by 3 and get 6.
then multiply the two ones digits, and get 21.
the answer is 621.
Yes, here's a proof. Let a be the common tens place digit (2 in this case), and b one of the ones place digits (either 3, or 7 in this case). Then
[tex](10a + b)(10a + 10 - b)[/tex]
[tex]= 100a^2 + 100a - 10ab + 10ba + 10b - b^2[/tex]
[tex]= 100a(a + 1) + b(10 - b)[/tex]
That is to say, multiply a by the next number up, multiply by 100 and add the product of the two numbers in the respective ones places.
 

1. How is it possible to do multiplication without a calculator or paper in just 10 seconds?

It is possible to do multiplication quickly without a calculator or paper by using mental math strategies and tricks. With practice, one can develop the ability to quickly estimate and solve multiplication problems in their head.

2. What is the best mental math trick for multiplying large numbers quickly?

One popular trick for multiplying large numbers quickly is the "split and multiply" method. This involves breaking down the numbers into smaller, easier-to-multiply parts and then adding the products together.

3. Can you provide an example of using mental math to multiply two large numbers quickly?

Sure, let's take 1565 and 1197 as an example. First, we can break down 1565 into 1500 + 60 + 5, and 1197 into 1100 + 90 + 7. Then, we can multiply each part and add them together: (1500 x 1100) + (1500 x 90) + (1500 x 7) + (60 x 1100) + (60 x 90) + (60 x 7) + (5 x 1100) + (5 x 90) + (5 x 7) = 1650000 + 135000 + 10500 + 66000 + 5400 + 420 + 5500 + 450 + 35 = 1863905.

4. Are there any other mental math strategies for multiplying large numbers quickly?

Yes, there are several other strategies such as the lattice method, the Russian peasant method, and the grid method. These methods involve breaking down the numbers into smaller parts and using visual patterns to solve the problem.

5. How can I improve my mental math skills for multiplying large numbers quickly?

The best way to improve mental math skills for multiplication is through practice. Start by practicing with smaller numbers and gradually work your way up to larger numbers. Also, try to memorize common multiplication facts to make the process faster. Additionally, there are many online resources and apps available for mental math practice.

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