What is the volume of a certain rectangular solid?
1 two adjacent faces of the solid have areas 15 and 24
2 each of two opposite faces of the solid has area 40
in a certain 2-digit integer, the ratio of the units digit to the tens digit is 2 to 3, what is the integer?
1. the tens digit is 3 more than the units digit
2. the product of the two digits is 54
is x negative?
1. n3(1-x2)<0 （n3,x2都是乘方，我不会打）
2. x2-1<0作者: tongxun 时间: 2002-11-22 18:49
1、条件1）ac=15，bc=24；or ac=15，ab=24。we cannot get what exactly abc is。thus this condition is insufficient。
condition 2）每两个相对的面的面积都是40。则ac=bc=ab=40。
因此，选B。
2、若数字为：AB，则 3B=2A
条件1）A-B=3， 则B=6，A=9 条件充分。
条件2）AB=54， 3AB=3*54，A=9，B=6
所以，选D。
3、条件1） n<0, 1-x^2<0. (1-x)(1+x)<0 => 1 (x-1)(x+1)<0 => x<1 or x> -1 this condition is insufficient too.
1+2: 也不能确定，所以选E作者: tongxun 时间: 2002-11-22 21:30
哪位兄弟帮我验证一下？谢谢了。作者: 猫猫头 时间: 2002-11-22 21:42
(1)i choose B
(2)D is right
(3)according to (2)x^2<1,so the key should be E作者: tongxun 时间: 2002-11-22 21:44
What is the volume of a certain rectangular solid?
1 two adjacent faces of the solid have areas 15 and 24
2 each of two opposite faces of the solid has area 40
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这个题目中的两个条件让人十分困惑。
条件2）中的each of two opposite 是指所有的面都这样吗？
若这样的话，条件2）就与条件1）有冲突。但不这么理解怎样理解？作者: 猫猫头 时间: 2002-11-22 21:45
1.why not A?
since "two adjacent faces of the solid have areas 15 and 24"
then the common factor of 15 and 24 is 3.
so the volume is 5x8x3(the adjacent side)
Isn't it an alternative way to solve the question?作者: viv614 时间: 2002-11-22 22:30
redhat： Thanks for your path to resolve this probelm！ but you answer is wrong。
the answer must be C。
Because the length of side probably is not a whole number， if the opposite area is 40， we can get the length of the side must be whole numbers such as 3、5、8。Therefore， the volume is 3*5*8
Could you do me a favor to work out the others？ thanks in advance。作者: 猫猫头 时间: 2002-11-22 22:37
