Re: [計量] Data sufficiency 請教

看板GMAT (GMAT入學考試)作者dounts (忘記過去)時間15年前 (2011/03/02 20:33)推噓0(0推 0噓 0→)

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※ 引述《Europe (extravaganza)》之銘言： : 來源為OG12 有一部分是題目看不懂 @_@ 先謝謝各位 : 128. : A school administrator will assign each student in a group of n students to : one of m classrooms. If 3<m<13<n, is it possible to assign each of the n students to : one of the m classrooms so that each classroom has the same number of students assigned : to it? 題目就是問 n/m is an integer? (m 是否可以整除 n) : 1) It is possible to assign each of 3n students to one of m classrooms so : that each classroom has the same number of students assigned to it. 3n/m = k 是整數 --> n/m = k/3 is an integer? 所以我們要確定 k 是 3 的倍數才行由條件可知 3n = mk 如果 n 不是 3 的倍數但是 m 是的話那就不能確定 k 是不是 3 的倍數了 : 2) It is possible to assign each of 13n students to one of m classrooms so : that each classroom has the same number of students assigned to it. : Answer: B 13n/m = k 是整數 --> n/m = k/13 is an integer? 所以我們要確定 k 是 13 的倍數才行由條件可知 13n = mk 由於 m < 13, 我們確定 m 不是 13 的倍數所以 k 一定為 13 的倍數 n/m = k/13 is an integer 這題更快的想法但不好用寫的來表達的方式是因為 m 可能是 3 的倍數所以 x3 可能會讓本來不是整數的答案變成整數但是 m 不可能是 13 的倍數所以 x13 基本上是不會改變是否為整數的結果 : 124. : Favorable Unfavorable Nor sure : Candidate M 40 20 40 : Candidate N 30 35 35 : 以上此表表示100個投票人的意見。What was the number of voters who responded : "Favorable" for both candidate? : 1) The number of voters who did not respond “Favorable”for either candidate : was 40. : 2) The number of voters who responded “Unfavorable”for both candidates was : 10. : Answer: A 將答案分成 "Favorable" and "Not favorable" 我們畫圖表示以 Yes/ No 做簡寫並且以 M 當成第一個判斷依據 Candidate M Candidate N Yes Yes ---> A ---> 40 No ---> B 100 Yes ---> C ---> 60 No No ---> D 所以我們要求出 A 且從 Candidate N 資料得知 A + C = 35 (A, C 代表對 Candidate N "Favorable") (1) 對兩者都不 Favorable 有 40 人 D = 40, --> C = 60 - 40 = 20 A = 15 (2) D 包含了 Unfavorable 和 not sure to both candidates Both Unfavorable 只是 D 的一部份所以依然求不出 D --> not sufficient : 161. : Beginning in January of last year, Carl made deposits of $120 into his : account on the 15th of each month for several consecutive months and then : made withdrawals of $50 from the account on the 15th of each of the remaining : months of last year. There were no other transactions in the account last : year. If the closing balance of Carl’s account for May last year was $2,600, : what was the range of the monthly closing balances of Carl’s account last : year? : 1) Last year the closing balance of Carl’s account for April was less than : $2,625. : 2) Last year the closing balance of Carl’s account for June was less than : $2,675. : Answer: C 按照月份 1 2 3 4 5 6 7 8 9 10 11 12 $2,600 我們只要知道從哪個月份"開始"提錢就知道了條件 1: 四月份金額 < 2625 四月份只可能有兩個金額一個是 2,480 (五月存錢) 一個是 2,650 (五月提錢) 很明顯四月份的金額是 2,480 所以五月份是存錢的條件 2: 六月份金額 < 2625 六月份只可能有兩個金額一個是 2,720 (六月存錢) 一個是 2,550 (六月提錢) 很明顯四月份的金額是 2,550 代表六月提錢兩個條件個別都無法求出哪個月份"開始"提錢但合在一起就知道五月存錢六月提錢所以我們可以求出 Balance 的 Range -- GMAT、各金融證照資訊交流 - 勇闖夢想的新鮮人 http://ndxica.pixnet.net/blog -- ※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 111.248.220.31 ※ 編輯: dounts 來自: 111.248.220.31 (03/02 20:36) ※ 編輯: dounts 來自: 111.248.220.31 (03/02 20:38)