Re: [計量] 請教幾題計量問題

看板GMAT (GMAT入學考試)作者Merica (美加文教)時間15年前 (2011/05/06 17:21)推噓0(0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~"~> 1.5 standard deviation from the arithmetic mean的意思是 mean+1.5倍的standard deviation = 46 + 1.5 x 4 = 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 2^n = n^2 n=2 2^2 = 2^2 n=4 2^4 = 4^2 只有n=2,4才符合 : 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 (8!) / (4!4!) = (8x7x6x5) / (4x3x2) = 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 此題記不完整，原題在GMAT Quantitative Review 2nd Edition P.85 第175題 : 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> 題意是說：為了確定所抽出卡片數字總和肯定是偶數，最多必須抽出幾張？假設很幸運，抽出第一張是偶數，那就不必再抽了，但若不幸，抽出第一張是奇數，且再抽出的第二張是偶數，總和還是奇數，假設再連抽9張偶數，每抽新的一張偶數和前面的總和仍然是奇數，等到把1~20的10張偶數抽完了，再抽第12張，肯定是奇數，和前面11張總和的奇數相加，奇數+奇數，就能肯定是偶數了。例如抽出的前12張為：1,2,4,6,8,10,12,14,16,18,20,3 所以答案是(B) : 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 : Thanks for your time and help ~ 設property value = x tax rate = y 原tax = xy 後tax = 0.9x(1.1y) = 0.99xy xy - 0.99xy = 0.01xy = 1%xy （以上內容由美加黃冠文老師提供） -- ▅▅▅▅ ▅▅ ▅▅▅ ▅ ▅▅ ▅▅▅ █ █ █ █▅ █▄█ ▄ █ █▄█ █ █ █ █▄ █◥▅ █ █▅ █ █ -- ※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 1.160.26.6 ※ 編輯: Merica 來自: 1.160.26.6 (05/06 17:23) ※ 編輯: Merica 來自: 1.160.26.6 (05/06 17:24)