作者chunning (机经达人)
看板GMAT
标题[问题] 请问两题有关PP的数学
时间Tue Feb 24 22:06:00 2009
这是PP1的第142题
The rate of a certain chemical reaction is directly proportional to the square
of the concentration of chemical A present and inversely proportional to the co
ncentration of chemical B present. If the concentration of chemical B is incre
ased by 100 percent, which of the following is closest to the percent change in
the concentration of chemical A required to keep the reaction rate unchanged?
(A) 100% decrease
(B) 50% decrease
(C) 40% decrease
(D) 40% increase
(E) 50%
ans:D
第二题为PP2的第117题
There are 8 magazines lying on a table; 4 are fashion magazines and the other 4
are sports magazines. If 3 magazines are to be selected at random from the 8
magazines, what is the probability that at least one of the fashion magazines w
ill be selected?
(没有选项及答案XD)
请知道如何解这两题的大大帮个忙
谢谢^^
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1F：推 kuo42:142.化学反应速率与 A物质数量的平方成正比；B物质数成反比 02/24 22:24
2F：→ kuo42:B 增加了1倍，为使速率维持不变，所以A平方也要同时增加1倍 02/24 22:26
3F：→ chunning:第一题了解!感谢k大^^ 02/24 22:30
4F：推 kuo42:117. 1-C4,3/C8,3 = 1-4/56 = 13/14 02/24 22:39
5F：→ kuo42:C4,3 => 3本皆选运动杂志 ； C8,3 => 全部组合数目 02/24 22:42
6F：→ kuo42:13/14 => 1 - 全部不选fashion 杂志的机率 02/24 22:43