GRE数学易错题Word文档格式.docx

1、a2表示a平方，a3表示a立方7新定義的運算ab=a（a+b）, 那a（ab）=a（aa+ab）=a（a+aa+ab）=aa+aaa+aab8.secretary typed 6 letters,each of which had either 1 or 2 pages.If the secretary typed 10 pages in all, how many of the letters had 2 pages?A 1 B 2 C 3 D 4 E 5答案是D，題目我都看不懂，是啥意思呢？這是說秘書打六封信，沒一封信要1頁或者兩頁。如果秘書總共打了10頁，那麼有多少封信是兩頁？解答：設有

2、x封，則2x+（6-x）=10,解得x=4.9 how many of the five numbers above are each equal to the product of an integer and an odd integer that greater than 1?這五個數是:2 6 8 14 16a.none b.one c.two d.there e.four我覺得這道題除了2不可能,其它四個數都有可能.可答案是c,想問大家為什麼?題目意思是這5個數哪些可以是2個1的數的積,一個是奇數,一個是整數,只有6和14的因數中有奇數,所以C.10 這句話大家看該怎樣列式子呢?這是

3、一道圖表題.what was the approximate percent increase in personal income from 1965 to 1970?是這樣（1970-1965）/1965還是（1970-1965）/1970這樣?是這樣:（1970-1965）/19651 the sum of two numbers, x and y, equals twice their products. if x=3, what is the value of y?這道題沒大看懂?請問大家是這樣麼?x+y=2（x+y）x+y=2xy,求y.2 if x is an integer a

4、nd x2（x的平方）90 度，比較三角形的周長與3倍AC的長度的大小，答案是BAC是最大邊,所以AB+BC+ACAC+AC+AC（3AC）.2.0p=2p（1-p）1/2 = p（1-p）=1/4 1/24 for the line with equation y=ax+b,the x-intercept os twice the y-intercept比較the slope of the line 與12的大小，答案是D，但算出來是12呀還有截距為零的情況,所以D.5 a certain moneymarket account that had a balance of $48000 du

5、ring all of last monthearned $360 in interest for the month. at what simple annual interestrate did the account earn interest last month?答案是9%,題目沒看懂意思是一個貨幣市場上個月共結餘48000，用它賺了360的利息，問以年單利計算每年利率是多少？360*12/48000=9%6 Of the positive integers that are multiples of 30 and are less than or equal to 360,what

6、 fraction are multiples of 12?a.1/6 b.1/5 c.1/3 d.2/5 e.1/2首先這道題我是對multilples of .不大明白,這是什麼意思啊?其次這道題怎麼解呢?在小於360的30的公倍數中,也是12的公倍數的占多少?30N360, 得N12,所以共有12個數滿足題幹.又12與30的最小公倍數為60,其實此題是求是60的倍數又小於等於360所占比例,同理求出為6所以,6/12=答案E7 A certain teacher has a total ofat least 110 students enrolled in her classes.if

7、the teachers has anaverage （arithmetic mean） of exactly 27 students enrolled per class.what is the least possible number of classes that the teacher couldhave?a.3 b.4 c.5 d.6 e.7我覺得這道題就是用110除以27就好了,可是答案是選c的是呀，110/27=4.04,如果是4個班，那麼總人數為108，還剩2個。當然是5個班了。8 a delivery service charges $0.02 per ounce for

8、the first 16 ounces ofa shipment and $0.15 for each additional ounce of theshipment,（1pound=16ounce）the delivery charges for x shipments weighing a combimed total of the pounds vs 567.00這道題答案選的是D,不明白怎麼會無法確定呢?我是這樣算的:160.2+（25*16-16）0.15.這樣對麼?因為x是個未知數，所以你無法確定它的值。9 the cost per gram of carrots if 3 can

9、s of carrots cost $0.90 the costper gram of onions if 5 cans of onions cost $1.50無法確定，沒有告訴1can有多少克？10 X is an integer, and the remainder when 2X is divided by 4 is 0. The remainder when X is divided by 4 0 選D，當x=2，-2時，餘數為2，-2，其它情況為01 LetX=3, if X is an odd integer; letX=6, if X is an even integer. r

10、 and s are integers, 3r is odd and 5+s is odd. r s3r是奇數說明r為奇數，所以r等於3，5+s為奇數，說明s為偶數，所以s=62 the value of the units digit in 647（6的47次方） the value of the units digit in 577（5的77次方）比較兩個數的個位，6不管多少次方個位都為6，5不管多少次方個位都為5.3 for all numbers r and s, where s/=（不等於）0, r#s=10r/s. 0.01#0.01 10.01#0.01=10*0.01/0.01

11、=10,大於1.4 1n5,n is an integer. the sum of the first n odd integers that are greater than zero n2（n平方）-1說的是n個大於零的奇數和。當n=2，1+3=4；n2-1=3;當n=3，1+3+5=9;n2-1=8;當n=4，1+3+5+7=16；n2-1=15所以選A5 a7+a15 a8+a14注是a的7次方,類推呵呵比較大小題後-前=a7（a-1）+a14（1-a） =（a7-a14）（a-1）然後討論,最後結果是後-前的差0,但當a=1時，相等。所以選D.6 A total of $480 is

12、 ina certain cash register. All of the money is in one-dollar and five-dollar bills, and there are 30 more one-dollar bills than five-dollar bills.The sum of 30 and the number of five-dollar bills in the cash register 105let x be the number of one-dollar bill y be the number of five-dollar billx+5y=

13、480-1x=y+30-2subsitute 2 in to 16y = 450so y=7530+75=1057 If N is an integer, then the units digit of N平方 cannot bea 0b 2c 4d 5e 6誰能把題目翻譯以下？謝謝就是N2的個位數不能為幾，應該選B吧8 the value of the units digit in 6的47次方 the value of the units digit in 5的77次方哪個大呀？這種題怎麼做呀？還有，黃皮書的答案是全對的嗎？怎麼有些明顯好怪的，望指點哈這是比較6的47次方的個位數與5的77

14、次方的個位數的大小。6的多少次方個位數都為6，5的多少次方個位數都為5.所以前面大於後面。選A。9 two successive discounts of 20percent and 40percent are equavilent tp a single discount of X percent. X 52同問此題，不明白題目說什莫 我理解的阿：打折20%後再打折40%，結果等於打一個X折，比較X和52的關係（100-20）*（100-40） = 48X = 100 - 48 = 5210.已知：y=x2-16x+64比較the least value of y和0的大小答案是C, y 沒

15、有最小直呀？y=（x-8）2,所以y的最小值為0.1 比較The remainder when a positive odd integer divided by 2The remainder when a positive even integer is divided by 2答案是A, 我覺得應該是B呀？奇數除2餘數必為1，偶數除2餘數必為零，選A2 If x,y,and z are consecutive positive integers, with xyz and x+y+z an even number, which of the following could be the v

16、alue of z?A.1 B.2 C.4 D.5 E.8答案是D,如果是D的話，那麼3+4+5也不是奇數呀？我覺得C和E怎麼都對呀？even是偶數的意思，三個連續的整數相加為偶數，則中間的書必為偶數，兩邊的就為奇數了。所以選D。3 In a group of 80 students,24 are enrolled in geometry , 40 in biology, and 20 in both. If a student were randomly selected from the 80 students, What is the probability that the strde

17、nt selected would NOT be enrolled in either course?我沒頭緒 沒學過概率，怎麼辦呢？這裡24個學幾何，40個學生物，20個全學。問兩個都沒學占多少比例。單學幾何的有24-20=4個，單學生物的有40-20=20個，所以學了這兩門的任何一門的有：20+4+20=44個。所以沒學的就是80-44=36個。所以概率為：36/80=9/20.4 triangular garden ABC is redesigned by increasing the length of AC by 20 percent to point C and decreasin

18、g the length of AB by 20 percent to B.the area of the original garden ABC the area of the redesigned garden ABC三角形ABC的面積：AC的長度乘以AB的長度。三角形AB的面積：1.2AC的長度乘以0.8AB的長度=0.96三角形ABC的面積5 一個三角形的三邊分別是11，5，13，怎麼判斷13的邊所對的角是鈍角？假設11， 5是兩條直角邊，斜邊的平方等於 146小於13的平方，所以13對的邊是鈍角Rectangle R has an area of 60 square units an

19、d a perimeter of 64 units. The length of the shortest side of R is x and the length of the longest side of R is y.問x/y大還是1/15大？這種題怎麼算呀，答案是一樣大xy=60x+y=32.得出：x=30,y=2和x=2,y=30.因為y大於x，所以x=2,y=306 Each of the following numbers has two digits blotted out.Which of the numbers could be the numbers of hours

20、 in x days, Where x is an integer?a.25*,*06b.50*,*26c.56*,*02d.62*,*50e.65*,*20P.S. * 代表blotted digit咋做呀這是求下麵哪個數能被24整除。當尾數為2，6時，倒數第二個數應該為奇數。當尾數為0，4，8時，倒數第二個數為偶數。所以選E。7 Three solid cubes of lead, each with edges 10 centimeters long, are melted together in a level, rectangular-shaped pan.The base of t

21、he pan has inisde dimesions of 20 centimeters by 30 centimeters, and the pan is 15 centimeters deep.If the volume of the solid lead is approximately the same as the volume of the melted lead,approximately how many centimeters deep is the melted lead in the pan?這道題實在沒大看懂,盼望牛人解釋.三個鉛塊,每個邊長10cm,熔了之後放在一矩

22、形平底鍋內.鍋的底面積2030,高15.問這三個熔了的鉛塊倒進鍋了有多深?8 On Elm Street are 6 houses on oneside of the street and 4 houses on the other.Each pair of houses on Elm Street is connected by exactly one telephone line.The total number of each lines that connect houses on opposite sides of Elm Street 12這道題我是思這麼想的:（6-1）+（4-1

23、）=8 而答案選的是A.你理解錯了,題目求連接街道兩面的電話線有幾根? 24個?,因為有一邊就4棟房子啊,46.9 100xy 1000x2y問:1100x y這道題我是沒有什麼思路,請大家幫忙.由上兩式知道xy/500,所以1100x （a2+b2）/a+b a+b（a2+b2）/a+b=a+b-2ab/a+b當a,b都大於零時，前者小於後者；當a,b都小於零時，前者大於後者。4 圖畫不出來。一個三角型，2條邊為X，一條邊為Y，邊Y上的高把三角形分成兩半，問一半的面積和xy/4，哪個大？（答案是xy/4大）設Y上的高為h，一半的面積為：1/2*1/2*y*h=y/4*h.所以比較的就是h和x

24、的大小。因為h是這個三角形的直角邊，而x是斜邊。所以h小於x，所以xy/4大。5 The water level in a tank is lowered by 6 inches, then raised by 8 inches, and then lowered by 4 inches. If the water level was x inches before the changes in level, which of the following represents the water level, in inches, after the changes?a. X-1.5 B.X+

25、1.5 C.X-6.5 D. X+6.5 E. X-18.5答案選A題目沒有說明 x的大小。有可能X6 .而除A外，其他答案都是不可能的。6 If the cube of n is 180 greater than the square of n, then n=?A. 10 B.9 C.8 D.7 E. 6答案選En三次方值比n平方值大180，如果解不出來，一個個帶入就行了。7 一個邊長為3 feet 的立方體頂面ABCD由對角線AC將立方體分開兩個相等的部分，問分開的一部分每個面的總面積和36 square feet 之間的大小？答案為：，但是我算出來應該是相等？5 個面， 應該是大於36， 有一邊是3sqrt（2）8 A certain five-number committee must be assembled form a pool of 5 women-A,B,C,D,E, and three menX,Y,Z, wh