Category: Mathematics

Multiply two 3 digits numbers in your head

April 22nd, 2008 | 8 Comments | Print

This article will show how to do multiplication of two three digits numbers from right to left. Consider 234 × 456.

Step 1: Multiply the last digits. Write 2, carry 4.

Step 2: Cross multiply the one and the tenth, and add them together. We get 53. Add the 4 that we carry to 53. We get 57. Write 7, carry 5.

Step 3: Multiply all digits, like in the figure below. We get 55. Add the 5 that we carry to 55. We get 60. Write 0, carry 6.

Step 4: Finally, multiply the two left digits. We get 22. Add the 6 that we carry to 22. Write 2, carry 2.

Step 5: Finally, multiply the left digits. Add the 2 that we carry to 8. We get 10. Write both numbers.

Therefore, the answer is 108072.

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8 Responses to “Multiply two 3 digits numbers in your head”

  1. Kujie says:

    Terimakasih… berminatnya saya.

    saya telah bookmark web ini untuk anak saya

  2. Selinap says:

    Kujie: Thank for bookmarking.

  3. NoktahHitam says:

    isnt this the same as multiplying using the normal method, only a little fancy.

    Not many can calculate this using head. We invented calculators, use it :p

  4. Selinap says:

    Actually, it is a bit faster to calculate this way. For instant, if you notice, we no more have the three rows, like normal multiplication of 3×3.

    With just a little practice, you could impress others.

    Why would you want to do that?

    Suppose that you are a marketing executive. It would be great if you could give an instant conclusion for a list of numbers. Isn’t it?

    Just my 2 cents.

  5. Adila says:

    nice! a great tip! why didn’t i come across before?
    i took a math module before where no calculators are allowed during the exam LOL
    so, my lecturer teached me this way..
    i’m using your example btw ^^

    237 x 456
    make it simpler as :
    237 x 400 = 94800 — 1
    237 x 50 = 11850 — 2
    237 x 6 = 1422 — 3

    add all the answers (1 + 2 + 3) together and you’ll get the same answer ^^

    it’s one of many ways to make difficult question seems easy :P

    that way helped me a lot since i’m such a careless person when calculating more than 2 digits LOL

    do share more math tricks please! :D

    Adilas last blog post..Old Mates II

  6. Selinap says:

    Adila: IMHO, this technique is the same as normal multiplication.

    What you do is separating the rows, and add zeroes at the back according to one, hundreds and thousands.

    In normal multiplication technique, we just add empty spaces instead of zeroes.

    BTW, perhaps this technique could be useful for people that cannot see between the lines, as an alternative.

    Some people can see clearly from one window, while the others might have seen clearer from the other window.

  7. Flug says:

    This looks really complicated, I don’t think I could do it in my head. I also rather stick to calculators :-) Since there’s even one on every cell phone, that makes it a lot easier…

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