[求助] gwd15-28, 35

TASSEL

Q28:  A school administrator will assign each student in a group of n student to one of m classrooms. If 3<m<13<n, is it possible to assign each of the n students to one of the m classrooms so that each classroom has the same number of students assigned to it?

(1) It is possible to assign each of 3n students to one of m classrooms so that each classroom has the same number of students assigned to it.

(2) It is possible to assign each of 13n students to one of m classrooms so that each classroom has the same number of students assigned to it.

Answer: B

Q35:  For what percent of those tested for a certain infection was the test a accurate; that is, positive for those who had the infection and negative for those who did not have the infection?

(1) Of those who tested positive for the infection, 1/8 did not have the infection.

(2) Of those tested for the infection, 90 percent tested negative.

Answer: E 

第一题不知何处下笔，第二题云里雾里不太明白是啥意思。求NN解答，谢谢！

[此贴子已经被作者于2009-4-6 17:42:37编辑过]

vivien_hu

第一题就问

n是不是m的倍数

1）3n是m的倍数 m是6  n是14就是反例啦

2）13n是m的倍数，因为m<13  所以n是m的倍数

我怎么觉得答案是B呢

vivien_hu

一共四种情况

test是p，实际是p  准确

test是p，实际是n  不准确

test是n，实际是p  准确

test是n，实际是n  准确

给出的两个条件还要加上test 是n  ，它的百分比有多少是p或是n

TASSEL

以下是引用vivien_hu在2009-4-6 17:24:00的发言：

第一题就问

n是不是m的倍数

1）3n是m的倍数 m是6  n是14就是反例啦

2）13n是m的倍数，因为m<13  所以n是m的倍数

我怎么觉得答案是B呢

是啦，不好意思，发错了。

解释很详细，谢谢！