Wild About Math! Making Math fun and accessible


Mathcast #3: Quick multiplication of two 3-digit numbers

Here's the You Tube Video that follows up Mathcast #2: Quick multiplication of two 2-digit numbers. The algebra of cross-multiplication explains how this method is derived.

If you enjoy this video check out all of the Wild About Math! mathcasts.


Comments (8) Trackbacks (2)
  1. OK, now that changes things. I definitely will practice a bit so that I can keep this as another tool. I can handle at least 4-digit x 4-digit this way, which extends my mental multiplication.

    I still look at, for example, 234 x 567 and see 234x7x3x3x3x3. Multiplying by one small digit seems the easiest option for me, when it exists.

    From time to time I share ‘tricks’ (techniques) with kids. I’ll let you know, when it comes up, how it goes.

  2. Jonathan,

    Wow, I’m impressed you can factor numbers so quickly and easily. It’d take me a fair effort to keep track of all those factors of 567.

  3. The first nine and second nine are not so bad (sum of the digits…), but in this case I saw 560 + 7 first, clearly 7 goes in.

    Three by three cross multiplication I think I can handle in my head now… but I still need to see the factors written in front of me.

  4. Hey Sol, I *actually* watched the whole video. I usually hate math… But this was really interesting. Thanks for the great content!


  5. @Jonathan – I also need to have the numbers in front of me when I do cross-multiplication but I can do it just like in the video 🙂

    @Alex – You’re quite welcome. Lots of people think they hate Math! I try to lure them away from that thought.

  6. Thank you! I am now really enjoying math! 🙂

  7. Hai Iam Ameesh I like Maths very much my favourite

    subject is Maths I want to do easy multiplication

    of three digits in mentally .

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