9Dec/078

## 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.

JonathanDecember 9th, 2007 - 13:11

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.

SolDecember 9th, 2007 - 17:51

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.

JonathanDecember 9th, 2007 - 21:26

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.

Alex KayDecember 11th, 2007 - 10:37

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

Alex

SolDecember 11th, 2007 - 19:43

@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.

program indir webmasterJune 30th, 2008 - 11:06

Idont look is video :S

PaulaJuly 10th, 2008 - 06:36

Thank you! I am now really enjoying math!

Ameesh J SurendranSeptember 9th, 2010 - 22:38

Hai Iam Ameesh I like Maths very much my favourite

subject is Maths I want to do easy multiplication

of three digits in mentally .