Re: [計量] 幾題數學~~

看板GRE作者bluecsky (我要藍藍淡淡的天空)時間17年前 (2008/06/17 15:41)推噓6(6推 0噓 10→)

留言16則, 4人參與討論串2/4 (看更多)

※ 引述《butini (hackneyed)》之銘言： : 救我的排列組合= =太爛了 : Test 5 : 10. Set X has x members and set Y has y members. Set Z i s composed of all : members that are in either set X or set Y with the exception of the k common : members (k>0).Which of the follow ing represents the numbers in set Z? : *看不懂k代表什麼? Ans: x+y-2k z : x + y 扣掉共有的 k : x y 中共有的... : Test 7 : 1.Each person at a party shook hands exactly once with each other at the : party. There was a total of 21 handshacks exchanged at the party. : Column A: the number of people at the part. : Column B: 8 : *我算7 選A 可是答案是B.. C(x,2) = 21 人數是7沒錯但是這題問題是比大小吧..所以選 b沒錯阿..8 > 7 : 20.Four boys and three girls are arranged seatts in two rows, the first : containing four seats and the second three seats. How many possible : arrangements are there if the boys and the girls sit next to each other? : Ans: 288 畫圖最快..(可惜我bbs畫圖能力是0) 簡單說明..男女要交錯坐..所以三個位置的排列一定是(男女男)(男可互調女位置固定) 四個位置的排列是(男女男女)(男女可互調男之間女之間也可互調) 決定三個座位 x 決定四個座位 C(4,2(男生)) x C(3,1(女生)) x 2!(男生位置互換) x C(2,2(男生)) x C(2.2(女生)) x 2(男女男女 and 女男女男) x 2!(男位置互換) x 2!(女位置互換) = 6 x 3 x 2 x 1 x 1 x 2 x 2 x 2 = 36 x 8 = 288 : 21. 同題20. How many arrangements are there if three girls sit together? : Ans:840 2種狀況三個都在三個座位那三個都在四個座位那三個都在三個座位 : 決定三個座位 x 決定四個座位 C(3,3(女生)) X 3!(女生互換) x C(4,4) x 4!(男生互換) =3! x 4! =6 x24 = 144 三個都在四個座位那 : 決定三個座位 x 決定四個座位 C(4,3(男生)) x 3!(男生互換) x C(1,1(男生)) x C(3,3(女生)) x 2(男女女女女女女男)x3!(女生互換) = 4 x 6 x 1 x 1 x 2 x 6 = 288 144+288 = 432..?..我算不出那個答案來.. 等一下我思考一下在算算看.. : Test 8 : 6.x+y+z<0 z>x+y+1 : Column A: z : Column B:1 : Ans:D : *有判斷的好方法嗎最簡單..隨意代數字進去看就知道.. : 8. On the real number line, the coordinate of points A, B, and C are 2, -1 : and x, respectively. What is value of x when line AC^2 + line BC^2 has : the least value? : Ans: 1/2 AC = BC的時候最小 : 21. If 5 cards, represented by A, B, C, D, and E, are placed in a row : so that C is never at either end, how many different arrangements : are possible? : Ans:72 : 我算96耶@@ 全部有5!種=120 C在最後面有4!種=24 120-24=96 : 那邊錯了?? C必須不在頭也不在尾..所以是24 x 2 = 48種(C在頭 or 尾) 120 - 48 = 72 : 22. How many possible committees can be formed from a group of seven people : if each committee can have any numbers from one to seven? : Ans: 127 2^7 - 1 = 128 簡單說就是..每個人只有兩種可能(加入跟沒加入委員會) 所以是2x2x2x2x2x2x2 - 1(全部都不加入) : Test 9 ex : "nine is the second power of three" Which of the following is the second power of (1+1^0.5)^0.5 1^0.5不就是1嗎?...所以原題目可以寫成..2^0.5..second power是同樣數字的乘積所以答案是 2 ??? : 24. A bag contatins red gloves, black gloves and white ones. : What is the least number of gloves that must be taken out of the bag : to be sure of having 4 pairs of gloves? : Ans:10 : *不懂最少要拿幾次才一定會有四對手套簡單說就是去討論一下..詳細算法還真難講..算是思考型的題目假使都不給面子一直湊不到最少幾次才能拿一雙..? 答案是..四次..(紅白黑任一) 用這樣去思考紅白黑 (任一,1雙) 跟前面同一顏色 (任一,1雙) 同前一顏色 (任一,1雙) 在同一顏色 (任一,1雙) 答案..10次..我是這樣想的啦.. -- 上帝曾經說過 : 當一個人打你右臉的時候你就要用日耳曼背橋摔壞它的左臉 -- ※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 118.169.209.212 ※ 編輯: bluecsky 來自: 118.169.209.212 (06/17 16:20) ※ 編輯: bluecsky 來自: 118.169.209.212 (06/17 16:22)

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qllvv

06/17 17:58, , 1^F

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butini

06/17 21:40, , 2^F

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bluecsky

06/17 21:46, , 3^F

06/17 21:46, 3^F