Re: [計量] A bowl contains red, green ...
看板GRE (GRE入學考試)作者sunrise5566 (想法很邪惡 行為很糟糕)時間17年前 (2009/02/17 20:14)推噓3(3推 0噓 4→)留言7則, 4人參與討論串2/4 (看更多)
※ 引述《eziya (...)》之銘言：
: 1. calumA: the number of odd positive factors of 30
: calumb: the number of even positive factors of 30
: 答案C
因式分解 1*2*3*5
a問 有幾個 奇數 因數 = 1,3,5,15 4個
b............偶數 = 2,6,10,30 4個
: 2.in how many ways can a, b, c, d, and e sit at a round table,
: if either b or c must sit in seat 1 and neither d nor e can sit 5?
: 1
: 5 2
: 4 3 不會畫圖，想像成圓桌
: ans:24
先 排c,d
先d不能做5,1也不行 所以 只剩3個(2,3,4)
接著e 只能2個(2,3)
再來a 沒限致做哪個 但不能做1 (2,5)
最後 b,c 做1 但有2種可能
3*2*2*2=24 看的懂嗎?
: 3.a bowl contains red, green and white balls. the probability of choosing
: a red ball is 1/3. there are 5 more green balls than red ones, and there
: are 12 white balls total. what is the odds against choosing a white ball?
: ans. 13/4
全部x
x(1/3)=red
g = r+5
w=12
x(2/3)=w+g = 12+x(1/3)+5 .....x=51
不會取到白/會取到白= (39/51)/(12/51) = 13/4
: 4. 1<n<5 n is an integer
: column A: the sum of the first n odd integers that are greater than zero
: Column B: n^2-1
: ans:A
a問前N個 奇整數 的和
n=2,3,4
n=2
a b
1+3=4 4-1=3
n=3
a b
1+3+5=9 9-1=8
n=4
a b
1+3+5+7=16 16-1=15
: 5. X= {2,3,4,5,6,7,8,9 }
: Y= {0,1}
: Z= {0,1,2,3,4,5,6,7,8,9}
: before 1990, telephone area codes in the united states were three-digit
: numbers of the form XYZ. shown above are sets X, y, z, respectively,
: were chosen. How many possible area codes were there?
: ans:144
這...恩 我發現這是講義題目
只是你的z= 0,1,2,3,4,5,7,8,9
^^^^^^^^^^^^^^^^^ 我的沒有6
8*2*9=144
: 感謝各位解答
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