2009年12月25日 星期五

乘法 video

http://hk.video.yahoo.com/video/video.html?id=68725

Example 1:
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e.g. 24 x 12 = 288 (利用劃線形式) = AB x CD

Step 1: 4x2 = 8 (AxD)
Step 2: 2x2 + 4x1 = 8 (AxD + BxC)
Step 3: 2x1 = 2 (AxC)

Answer = 288


Example 2:
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If ask "123 x 251", change the question as "251 x 123".

e.g. 251 x 123 = 30,873 (ABC x DEF)

Step 1: 1x3 = 3 (CxF)
Step 2: 5x3 + 1x2 =17 (BxF + CxE)
--> Greater than 10, then plus 1 to step 3, keep as 7
Step 3: 2x3 + 5x2 + 1x1 = 17 (AxF + BxE + CxD)
--> Greater than 10, then plus 1 to step 3, be 8
Step 4: 2x2 + 5x1 = 9 (AxE + BxD), change as zero, plus 1 to step 5
Step 5: 2x1 = 2 (AxD)

Answer = 30,873

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