新东方4册练习1 S5.(13题) 15页 我不太理解问题.
If a 3-digit integer is selected at random from the integers 100 through 199, inclusive, what is the probability that the first digit and the last digit of the integer are each equal to one more than the middle digit?
A.2/225 B.1/111 C.1/110 D.1/00 C.1/50 KEY: D ???
新东方4册练习2 S5.
S5 (15题) 35页 我不太理解问题.
(图形) 一相框,外沿长18,宽15.
The shaded region in the figure above represents a rectangular frame with length 18inches and width 15 inches. The frame cncloses a rectangular picture that has the same area as the frame itself. If the length and width of the picture have the same ratio as the length and width of the frames, what is the length of the picture, in inches?
A.9*根号2 B.3/2 C.9/根号2 D.15*(1-1/根号2) E.9/2 KEY.A ???
S7 (15题) 40页 我不太理解问题.
An infinite sequence of positive integers is called an "alpha sequence" if the number of even integers in the sequence is finite. If S is an infinite sequence of positive integers, is S an alpha sequence?
1) The fist ten integers in S are even
2) An infinite number of integers in S are odd.
KEY.E ???作者: tongxun 时间: 2002-9-10 18:27
If a 3-digit integer is selected at random from the integers 100 through 199, inclusive, what is the probability that the first digit and the last digit of the integer are each equal to one more than the middle digit?
A.2/225 B.1/111 C.1/110 D.1/00 C.1/50 KEY: D ???
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同意D。100-199，有100个数字，而符合条件的应该只有101。概率应该是1/100
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S5 (15题) 35页 我不太理解问题.
(图形) 一相框,外沿长18,宽15.
The shaded region in the figure above represents a rectangular frame with length 18inches and width 15 inches. The frame cncloses a rectangular picture that has the same area as the frame itself. If the length and width of the picture have the same ratio as the length and width of the frames, what is the length of the picture, in inches?
A.9*根号2 B.3/2 C.9/根号2 D.15*(1-1/根号2) E.9/2 KEY.A ???
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问题是这样的：一相框+相片=18*15， 其中相片的长/宽=18/15=6/5，求相片的的长。
18*15*（1/2）=6x * 5x，得X=（3根号2）/2。则长为6*（（3根号2）/2）=9根号2
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S5 (16题) 35页 请教解题思路
(图形) 横着4条街,竖着3条街,交叉共形成12个交叉点, 问从最左下角这点到最右上角这点走最短的路线, 有几种走法?
A.6 B.8 C.10 D.14 E.16 KEY. C ???
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C5，2=10。具体我给你查查书，再跟帖。
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S7 (15题) 40页 我不太理解问题.
An infinite sequence of positive integers is called an "alpha sequence" if the number of even integers in the sequence is finite. If S is an infinite sequence of positive integers, is S an alpha sequence?
1) The fist ten integers in S are even
2) An infinite number of integers in S are odd.
KEY.E ???
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答案应该没错。
条件1）咱们不知道S是否是An infinite sequence
条件2）不知道S是否是the number of even integers in the sequence is finite.
1）+2）。也不知道the number of even integers in the sequence is finite.。
所以选E作者: brigittew 时间: 2002-9-12 20:10
