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[Core] 5** Maths Question of the Day 1.7 (DSE數學奪5**必做題型!!!) [已附答案]

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first time 3600
2nd time 5640
..... 同好多人都唔同.......我數學一向差><

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3600?

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唔知係咪咁呢....3720
2013 DSE生
為未來加油!

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3360???

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My approach:
7!-2*6!+5!

[ 本帖最後由 leon592 於 2012-6-13 10:42 PM 編輯 ]
2013 DSE
PHY CHEM ECON +M2

5**: MATHS, M2, CHEM, ECON

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35 ?????

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其實樓主有無詳解?因為計黎計去都係3600-,-

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5!x6p2

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5P2 x 5P5 = 2400
please comment if the following explanation is correct(:
because "l" and "o" cannot be at their original positions, so from the remaining 5 letters,(i.e.: s, f, r, u, m) choose 2 out of them to be placed at the original positions of "l" and "o" --> 5P2
then from the other 5 letters remaining (including "l" and o), they can be placed at any of the remaining 5 positions, --> 5P5

thanks!

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7!-5!=4920係wo, 係
7!-6!x2+5!....=3720

[ 本帖最後由 henry407 於 2012-6-28 04:15 PM 編輯 ]

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l    s   f   o   r   u  m
原來是l和o是但一個都唔可以相同位置  睇漏
應該是 7! -2(5x5! ) - 5!

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(L is in 4th) + (O is in 1st) + (L in the 4th and O is in the 1st)
6P6 + 6P6 +5P5 =  1560

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Oh.. i am wrong...

For L to be in 1st.. 6!
For O to be in 4th .. 6!
but there ar some in common( L in 1th and O in 4th)
therefore 6! + 6! - 5! = 1320 <--- the combinations which is not correct..

7! - 1320 = 3720

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7!-6!-6!+5!=3720?

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4320?

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