[問題] 陳向東數學問題

看板GRE (GRE入學考試)作者 (Q仔)時間11年前 (2014/09/17 15:02), 編輯推噓3(309)
留言12則, 3人參與, 最新討論串1/1
大家好: 請教大家數學問題 陳向東P260 13.Each integer from 1 to 50 whose units digit is a 3 is written on a slip of paper and placed in a box. If two slips of paper are drawn at random, what is the probability that both the numbers picked are prime? 14. A jar contains 20 marbles: 4 red, 6 white, and 10 blue. If you remove marbles one at a time, randomly, what is the minimum number that must removed to be certain that you have at least 2 marbles of each colar? A.6 B.10 C.12 D.16 E.18(Ans.) P261 18 George earned 80, 85 and 90 on the first three tests in his G class.Becoz he didn't have time to study, he decided to guess randomly on the final test. That test has ten true-false questions, each worth 10 points. What is the probability his final average is more than 85? A. 12/2的八次方 B. 11/2的八次方 C. 12/1024 D. 11/1024(Ans.) E. 0.5 感謝! -- ※ 發信站: 批踢踢實業坊(ptt.cc), 來自: 180.177.48.63 ※ 文章網址: http://www.ptt.cc/bbs/GRE/M.1410937379.A.7B6.html

09/17 15:50, , 1F
最後一題 more than 85--> 可能有90 or 100
09/17 15:50, 1F

09/17 15:50, , 2F
每一題對的機率有1/2 共有十題 所以分母是2的十次方
09/17 15:50, 2F

09/17 15:51, , 3F
90分有10種可能(第一題錯or2...or.9 or第十題錯)
09/17 15:51, 3F

09/17 15:51, , 4F
再加上100的可能只有一種就是全對 所以分子是10+1
09/17 15:51, 4F

09/17 15:53, , 5F
第一題答案是4/5嗎? 如果是的話
09/17 15:53, 5F

09/17 15:53, , 6F
就是 把個位數是3的寫在紙上 然後從這些紙中抽出來
09/17 15:53, 6F

09/17 15:53, , 7F
有3,13,23,33,43 其中是質數的有3,13,23,43
09/17 15:53, 7F

09/17 15:53, , 8F
所以就是4/5
09/17 15:53, 8F

09/17 16:03, , 9F
第3題瞭了,感恩! 第1題答案是寫3/5,難道答案錯!?
09/17 16:03, 9F

09/17 16:06, , 10F
阿是我看錯 這些紙要一次抽兩張(剛看成抽一張)
09/17 16:06, 10F

09/17 16:09, , 11F
那就是 分子C4取2 分母C5取2
09/17 16:09, 11F

09/17 19:02, , 12F
0.6;E;D
09/17 19:02, 12F
文章代碼(AID): #1K6J8ZUs (GRE)
文章代碼(AID): #1K6J8ZUs (GRE)