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[計量] For how many intergers n is.....

看板GRE (GRE入學考試)作者 (櫻花茶)時間17年前 (2009/05/04 14:48), 編輯推噓4(4推 0噓 4→)
留言8則, 4人參與, 最新討論串1/3 (看更多)
1. For how many intergers n is [n / (20-n)] the square of an interger? A) 1 B) 2 C) 3 D) 4 E) 10 Ans: D 我在算這題是求出n=10,16,18 我還漏掉哪個數字呢?? 速解公式有嗎?? 2. x If N= (-2) , where x is a negative interger, M is the difference of the greatest value of N and the least value of N Column A: M Column B: 3/4 Ans: C 最大值我算1/4 可最小值我就不知怎麼算了... 還是我有哪裡弄錯呢@@ 3. For how many positive intergers n that is less than 1,000 has the property that the sum of digits of n is equal to 7? A) 24 B) 30 C) 36 D) 40 E) 43 Ans: C 有速解公式嗎?? 還是只能一個一個算?? 而且我一個個算也是算出30阿... 4. Column A: The reciprocal of (1/2 + 1/3) Column B: 根號2 ANS: A reciprocal不是倒數嗎?? 因此columnA 答案應是1.2, 就會比column B的1.414小阿... 為啥答案還是A>B @@ 有人可以解決這題的疑惑嗎? 5. Two people invested equal amounts of money for one year, one at 8 percent simple annual interest and the other at 12 percent simple annual interest. If after the one year the amounts of money invested plus interest differed by $50, what was the original amount invested by each person? A) $200 B) $250 C) $1250 D) $1350 E) $1400 Ans: B 我算C 我哪裡搞混咧?? 我的算式為:設原數X元 X(1+12%*1)-X(1+8%*1)=50 以上5題 懇請版友解惑>"< 感激不盡... -- ※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 61.228.107.216
推
05/04 14:58, , 1F
1. 0
05/04 14:58, 1F
→
05/04 15:15, , 2F
為啥是0?? 他算是一個平方數嗎??
05/04 15:15, 2F
推
05/04 15:37, , 3F
YES
05/04 15:37, 3F
推
05/05 01:18, , 4F
可以問2.最大值怎麼算嗎?
05/05 01:18, 4F
推
05/05 09:25, , 5F
最大值 x=2 N = 1/(-2)^2 = 1/4
05/05 09:25, 5F
→
05/05 09:26, , 6F
講錯~~~ x=(-2), N = 1/(-2)^2 = 1/4
05/05 09:26, 6F
→
05/05 09:28, , 7F
x=-1 N=-1/2; x=-2 N=1/4; x=-3 N=-1/8; x=-4 N=1/16
05/05 09:28, 7F
→
05/05 09:29, , 8F
由此可知x=-1&-2時有最小最大值，其後的值都在兩者間
05/05 09:29, 8F
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