问题
选择题
从8名女生,4名男生中选出6名组成课外小组,若按性别比例分层抽样,则不同的抽取方法种数是( )
A.C83C43
B.C84C42
C.C126
D.A84A42
答案
8名女生,4名男生中选出6名组成课外小组,
每个学生被抽到的概率是
=6 8+4
,1 2
按性别比例分层抽样
∴女生要抽取4人,男生要抽取2人,
∴不同的抽取方法是C84C42
故选B.
从8名女生,4名男生中选出6名组成课外小组,若按性别比例分层抽样,则不同的抽取方法种数是( )
A.C83C43
B.C84C42
C.C126
D.A84A42
8名女生,4名男生中选出6名组成课外小组,
每个学生被抽到的概率是
=6 8+4
,1 2
按性别比例分层抽样
∴女生要抽取4人,男生要抽取2人,
∴不同的抽取方法是C84C42
故选B.
Finally, a cell phone That’s… a phone With rates as low as $3.75 per week ! “Well, I finally did it. I finally decided to enter the digital age and get a cell phone. My kids have been annoying me and the last straw was when my car broke down, and I was stuck by the highway for an hour before someone stopped to help. But when I went to the cell phone store, I almost changed my mind. The phones all have cameras, computers and a “global-positioning” something or other that’s supposed to spot me from space. Goodness, all I want to do is to be able to talk to my grandkids! The people at the store weren’t much help. They couldn’t understand why someone wouldn’t want a phone the size of a postage stamp. And the rate plans! They were confusing, and expensive… and the contract (合同)lasted for two years! I’d almost given up until a friend told me about her new Jitterbug phone. Now, I have the convenience and safety of being about to stay in touch with a phone I can actually use. ” Affordable plans that I can understand---and no contract to sign (签订)! Unlike other cell phones,Jitterbug has plans that make sense. Why should I pay for minutes I’m never going to use? And if I do talk more than I plan,I won’t find myself with no minutes like my friend who has a prepaid phone. Best of all, there is no contract to sign, so I’m not locked in for years at a time. The US-based customer service is second to none. And the phone gets service anywhere in the country.
Call 1-888-809-8794 or visit www.jitlerbugdirect. com. 小题1:What made “I” finally think of getting a cell phone?
|