我把我會算的寫出來 大家一起討論 ~~希望沒有錯才是~~3.
3.
1) 根據條件1 可得知 (x+y)/2 =5 ----> x+y=10---->且提中提到 X>Y and X and Y are positive integers.所以可知道
(y ,X) 分別可能組合為 (1,9) (2,8) (3,7) (4,6) 條件尚未足夠
2) 條件二得知 平均亦為正整數---->單純此條件尚未足夠
3) 但若是將條件一中這四組代入計算 (5x+3y)/8---->只有第一組 (1,9)可得整數....其餘都非整數 所以答案為C
5.
The tens digit of positive integer X is 3. Is the units digit of X greater than 4? (1) The units digit of 2X is less than the units digit of X.（--->將此X乘以二以後 他的各位數會小於原來的各位數---->暗示此個位數必>4，因為(1, 2, 3, 4) 乘2以後為(2,4,6,8）都大於原來的；但(5,6,7,8,9)乘2以後分別為(0.2,4,6,8)都小於原來的) 故調條件一單獨符合
(2) The tens digit of 2X is 7. 十位數原來為3但是乘以2以後成7，代表個位數乘以二以後一定會進位，所以個位數必為5以上 (5,6,7,8,9)，如此個位數乘二以後才會進位到十位數。故條件二單獨亦符合。
A 9 The operation* represents either addition, subtraction, or multiplication of integers, what is the value of 1*0? (1) 0*2=2 (2) 2*0=2
這題我怎麼覺得答案是D 總覺得 (1) 與 (2) 各都可以得到 1*0--->1 1) *必等於 "+" 2) *必等於 "+ 或者 -" 可是不論是+ - 都可以得到1
d21C
10 If
each of the 12 teams participating in a certain tournament plays
exactly one game with each of the other teams, how many games will be
played? A. 144 B. 132 C. 66 D. 33 E. 23
此題是C 12取2 的觀念 因為12teams彼此之間2組互比 但是不管先後 所以是 66
A 12 During
a 10-week summer vacation, was the average (arithmetic mean) number of
books that Carolyn read per week greater than the average number of
books that Jacob read per week? (1) Twice
the average number of books that Carolyn read per week was greater than
5 less than twice the average number of books that Jacob read per
week.（不知道什么意思）--->我的解讀是 2平均C - 2 平均J > 5 ---->所以條件一符合
(2) During the last 5 weeks of the vacation, Carolyn read a total of 3 books more than Jacob. 不知道後五週的關係 所以條件二不符合
If P and R are positive, is 25 percent of P equal to 10 percent of R? (1) R is 150 percent greater than P (2) P is 60 percent less than R. D 36
1) R-1.5----> R=2.5P
2) P=R-60%P---->1.6P=R
而題目中P and R are positive....我就任意取正整數代入 都可以各自得到結果 (不知道有沒有其他比較簡單的方法 ?
Mary
passed a certain gas station on a highway while traveling west at a
constant speed of 50 miles per hour. Then, 15 minutes later, Paul
passed the same gas station while traveling west at a constant speed of
60 miles per hour. If both drivers maintained their speeds and both
remained on the highway for at least 2 hours, how long after he passed
the gas station did Paul catch up with Mary? A. 30 min B. 45 min C. 1 hr D. 1 hr 15 min E. 1 hr 30 min
15分鐘以後 Ｍ已經開過了 15分鐘/60分鐘X50miles＝12.5miles
所以可以列式出
設Ｘ分以後Ｐ catch up Ｍ
12.5+50X =60X
故求得X＝1.25小時----> 1 hr 15 min
其他題 我實在不太確定 
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发表于 2009-4-11 16:50:00
