Re: [計量] 請教幾題計量問題

看板GMAT (GMAT入學考試)作者dounts (忘記過去)時間15年前 (2011/04/29 00:13)推噓1(1推 0噓 0→)

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※ 引述《Vucasee (Epsilon)》之銘言： : 小弟遇到幾個問題，煩請大大不吝指導。 : 題目是在GMAT 數學高分突破的數學機考模擬150題中的幾題。 : 書中只有答案但沒有詳解。 : 8. The arithemetic mean of a data set is 46 and the standard : deviation of the set is 4. Which value is exactly 1.5 standard : deviations from the arithmetic mean of the set? : (A) 42 (B) 44.5 (C) 47.5 (D) 50 (E) 52 : A: E : < 這種standard deviation 的題目常常會看不懂~"~> 用 standard deviation 嚇嚇你而已這題把 standard deviation 換成 x 也可 46 ±1.5 x, x = 4 代入得到 40 or 52 : 9. For how many integers n is 2^n = n^2 ? : (A) None (B) One (C) Two (D) Three (E) More than three : A: C 兩種解法：1. 直接硬代 --> n = 2 or 4 或者 2. 看到 2^n = n^2 --> Suppose n = 2^k 2^(2^k) = (2^k)^2 = 2^(2K) 2^k = 2k, k = 1 or 2 --> n = 2 or 4 不必太鑽研考到這樣複雜的計算概念機會不多 : 32. A first-grade teacher use ten flash cards, number 1 through 10, : to teach her students to order numbers correctly. She has students : choose four flash cards randomly, then arrange the cards in ascending : order. One day, She removes the cards number "2" and "4" from the deck : of flash cards. On that day, how many different correct arrangements of : four randomly selected cards are possible? : (A) 70 (B) 210 (C) 36 (D) 840 (E) 1680 : A: A 剩八張卡選四張不需要排列 (ascending) C(8,4) = 70 : 36. A square countertop has a quare tile inlay in the center, leavin an : untiled strip of uniform width around the tile. If the ratio of the tiled : area of the following could be the width, in inches, of the strip? : I. 1 II. 3 III. 4 : (A) I only (B) II only (C) I and II only (D) I and III only : (E) I,II and III : <看不懂題目在講什麼..> : A: E A square countertop has a square tile inlay in the center, leaving an untiled strip of uniform width around the tile. If the ratio of the tiled area to the untiled area is 25 to 39, which of the following could be the width, in inches, of the strip? http://www.beatthegmat.com/square-countertop-t21427.html 題目背錯囉！順道一提，我不喜歡這裡的解釋 GMAT 考這種題型不是要你算出答案的是問你有沒有可能性題目是指一個正方形的磚瓦附上非磚瓦的框架框架寬度一樣你給了我兩個面積的"比例" 我就可以求出兩者邊長的"比例" (小正方邊長 : 大正方邊長 = 5 : 8, 所以邊長比 5 : (8 - 5)/2 = 5 : 1.5) 以上通通不用計算！有比例沒數字那就是什麼情形都可以發生答案 all possible : 43. Jerome wrote each of the integers 1 through 20, inclusive, on a separate : index card. He placed the cards in a box, then drew cards one at a time : randomly from the box, without returning the cards he had already drawn : to the box. In order to ensure that the sum of all the cards he drew : was even, how many cards did Jerome have to draw? : (A) 19 (B) 12 (C) 11 (D) 10 (E) 3 : A: B : <但是如果7 odd + 5 even = 還是odd 啊, 沒辦法ensure 吧？＠＠我寫A> 自作聰明的出題法錯誤百出不用管他 : 60. If the value of a piece of property decreases by 10 percent while : the tax rate on the property increase by 10 percent, what is the : effect on the taxes? : (A) Taxes increase by 10 percent. : (B) Taxes increase by 1 percent. : (C) There is no change in taxes. : (D) Taxes decrease by 1 percent. : (E) Taxes decrease by 10 percent. : A: D value decreases by 10% --> tax * 0.9 tax rate increases by 10% --> tax * 1.1 so tax * 0.9 * 1.1 = 0.99 tax 選 (C) 的同學基本上沒考慮到第二次增加 10% 是以之前滑下 10% 做基準點基準點已經不同了所以結果不會跟一開始一樣在 GWD 也考過類似的題型 The annual rent collected by a corporation from a certain building was x percent more in 1998 than in 1997 and y percent less in 1999 than in 1998. Was the annual rent collected by the corporation from the building more in 1999 than in 1997? (1) x > y (2) xy/100 < x – y 答案 (B) 答案不選 (1) 的原因同上題基準點不同無法比較選 (B) 原因是因為如果把式子展開消掉就會得到 (2) 的結果式子真的很難用 BBS 寫帶不出來再寫信問我吧...... : Thanks for your time and help ~ 也謝謝你我的數學講義可以多放幾題加油!! -- 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: 111.248.212.133 ※ 編輯: dounts 來自: 111.248.212.133 (04/29 00:21)