38. 有10个Red marbles,30个Blue marbles。可放回,直至拿到2R or 2B。第一个拿的是R, 问下一个拿的是红的概率。它是问what’s the probability of the next be red before he selected 2 blues…. 我看不懂题目…
39. 有4个jars, 每个jar有m个marble。从第一个jar里移走一部分分别放到第二个jar、第三个jar、第四个jar。最后它们的marble比例为1:6:5:4。in terms of m, 移走了多少个?
45. a cube, a diagonal joining 2 vertices (not on the same face)…diagonal长? When edges=5cm …?大概是这样子滴…作者: myice 时间: 2010-6-30 23:19
46. Subscribe to A newspaper中有1/5也subscribe to B. Subscribe to B的有1/4 subscribe to A. What’s the fraction of those who subscribe to both to those subscribe to B?
50. A=2B, A=3C, A decreased by 2.5%, B decreased by 1.5% while C increased by 3%, 问改变之后的总和变化的percentage
(1) …忘记了…
(2) A+B+C=3600作者: myice 时间: 2010-6-30 23:19
91. DS: a, b, c, d 是四个个位正整数,some or all of which are equal。现在它们组成了3个两位数,ab cd bc,问:ab+cd = a+bc+d是否成立?
1)a=b-c
2) d=b-c (不太确定这个选项是不是这样的了)
其实不难,因为ab = 10a+b, cd = 10c+d, bc=10b+c, 题干中带入联立等式,最后等于9(a-b+c)=0,所以要等式成立,必须a=b-c,所以我选A