ChaseDream

标题: PP 2题数 怎么算 求救 [打印本页]

作者: lazyzoe    时间: 2010-5-25 17:26
标题: PP 2题数 怎么算 求救
{-10, -6, -5, -4, -2.5, -1, 0, 2.5, 4, 6, 7, 10}

A number is to be selected at random from the set above.What is the probability that the number selected will be a solution of the equation (x - 5)(x + 10)(2x - 5) = 0 ?

Ans: 1/6





Equal amounts of water were poured into two empty jars of different capacities, which made one jar1/4 full and the other jar 1/3 full.If the water in the jar with the lesser capacity is then poured into the jar with the greater capacity, what fraction of the larger jar will be filled with water?

Ans: 1/2

作者: jjc311    时间: 2010-5-25 17:35
第一题~方程的根分别是-10,2.5,5~而集合里面没有5,所以5这种情况可以忽略~
分情况讨论:
当X=2.5时,也就是从集合里面抽出2.5这个数,概率为1/12
同理,当X=10时,其概率也为1/12
将两种情况的概率相加:1/12+1/12=1/6

P。S求教第二题
作者: Nicewill    时间: 2010-5-25 18:51
第二题中注意“Equal amounts”,不用多去想1/3和1/4,他们是一样的体积,所以第一个罐里德谁水倒到第二个里也是第二罐的1/4,所以1/4+1/4=1/2
作者: bonnie0715    时间: 2010-5-25 18:55
第二题,第二次倒得和第一次倒得其实是一样的,乘以2就可以了
作者: lazyzoe    时间: 2010-5-25 19:02
谢谢




欢迎光临 ChaseDream (https://forum.chasedream.com/) Powered by Discuz! X3.3