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VCE Stuff => VCE Mathematics => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE General & Further Mathematics => Topic started by: monokekie on July 31, 2009, 05:53:03 pm

Title: 12x34=? (something i learnt today)
Post by: monokekie on July 31, 2009, 05:53:03 pm: (http://img338.imageshack.us/img338/6395/95109707.png)
Title: Re: 12x34=? (something i learnt today)
Post by: Over9000 on July 31, 2009, 06:25:13 pm: Quote from: monokekie on July 31, 2009, 05:53:03 pm
(http://img338.imageshack.us/img338/6395/95109707.png)
Just use ur calc, or 10x34 + 2x34 = 340 + 68 = 408.
A squarish thing wont help u much.
Title: Re: 12x34=? (something i learnt today)
Post by: dcc on July 31, 2009, 06:34:14 pm: I don't quite understand this square, but splitting up the multiplication as >9000 has done is the non-calculator method I would suggest (because we LOVE multiplying by 10).
Title: Re: 12x34=? (something i learnt today)
Post by: shinny on July 31, 2009, 06:55:48 pm: It's exactly the same as doing (yes, cbf latex)

34
x12
---
68
340
---
408

but on a slant, so you don't need to add the extra 0 in the fourth line. There's a much better way of mentally doing any two digit multiplication which I'd come across once, but can't quite remember how to do it.
Title: Re: 12x34=? (something i learnt today)
Post by: /0 on July 31, 2009, 08:23:42 pm: There is a cross-multiplying method for 2-digit numbers. You multiply the two numbers in the unit's column and put this as the unit's digit. Then you cross-multiply as shown in the example, putting this in the ten's, and finally multiply the two numbers in the ten's column and put this as the hundred's. Any remainders are carried over.

$\begin{array}{cc}\ \ 34 \\ \underline{\times 12} \\ 408\end{array}$

The $8$ is gotten by $2 \times 4=8$

The $0$ is gotten by cross-multiplying: $3 \times 2 + 1 \times 4=10 \ (carry \ the \ 1)}$

The $4$ is gotten by $1 \times 3 + 1=4$

Personally I always do it this way, except when I spot something nice like over9000 seems to always do
Title: Re: 12x34=? (something i learnt today)
Post by: Johnle on November 04, 2009, 02:23:06 am: Quote from: monokekie on July 31, 2009, 05:53:03 pm
(http://img338.imageshack.us/img338/6395/95109707.png)

I dont understand y drawing squares
Title: Re: 12x34=? (something i learnt today)
Post by: Visionz on February 05, 2010, 09:25:13 pm: 34
X12
4x2 = 8
30+10 = 40
408(34x12) O_O

27
x11
7x1 = 7
20+10 = 30
307 - 10 = 297 (27x11)

55
x17
5x7= 35
5+5-1 = 9
935 (55x17)

kthxbai
Title: Re: 12x34=? (something i learnt today)
Post by: physics on February 05, 2010, 09:26:53 pm: i don't get the square
Title: Re: 12x34=? (something i learnt today)
Post by: brightsky on February 05, 2010, 09:49:40 pm: Quote from: annahinh on February 05, 2010, 09:26:53 pm
i don't get the square

The question is 12 x 34.

For 34, you split it into 3 and 4 and draw 3 lines and 4 lines respectively as two opposite sides of the square.

For 12, you do the same thing, splitting 1 and 2.

As you can see in the picture, the numbers written on each corner correspond to the number of blue lines multiplied by the number of pink lines intersecting at the corner.

So arithmetically, the four numbers would be represented as:

$3 \times 100 + (6 + 4) \times 10 + 8 \times 1$

$\implies 300 + 100 + 8$

$\implies 408$

Tell me if I've got this wrong. :p
Title: Re: 12x34=? (something i learnt today)
Post by: the.watchman on February 05, 2010, 09:51:24 pm: Yeah it's right, but I'm not sure how useful it is.
It's just a visualisation tool really...
Title: Re: 12x34=? (something i learnt today)
Post by: brightsky on February 05, 2010, 09:52:20 pm: Quote from: the.watchman on February 05, 2010, 09:51:24 pm
Yeah it's right, but I'm not sure how useful it is.
It's just a visualisation tool really...

Yeah, another way of expressing long division. But instead of numbers, you do it with lines and colours! :)
Title: Re: 12x34=? (something i learnt today)
Post by: v3n0m on April 06, 2010, 09:18:00 am: I dont know why but i prefer long division better then short one. I gues that's how i grew up.