问题 选择题

有A,B,C三种零件,分别为a个,300个,b个.采用分层抽样法抽取一个容量为45的样本,A种零件被抽取20个,C种零件被抽取10个,这三种零件共(   )个

A.900

B.850

C.800

D.750

答案

答案:A

题目分析:先求出样本中C层所占的比例,则该比例是总体中C层得人数所占的比例,再根据此比例求出零件的个数.

由题意知,C种零件被抽取45-10-20=15个,样本中B层所占的比例是:,设总体中零件的个数为n,则,解得n=

故答案为A

点评:解决分层抽样的关键是理解,每层中各个个体被抽到的是等比例的,那么通过已知中零件B被抽到的数目和总数,就知道比例值了。属于基础题。

单项选择题 A1/A2型题
阅读理解

阅读理解

      Do you love the holidays, but hate the pounds that follow? You are not alone. Holidays are times

for feasting and celebrating. Many people are worried about their weight. With proper planning, though,

it is possible to keep normal weight during the holidays. Whether it is celebrating at the office party or

sitting down for the traditional family dinner, regard eating as a time for tasting a variety of the foods. The

idea is to enjoy the holidays but not to eat too much. You don't have to turn away from the foods that you enjoy.

     Here are some tips for preventing weight gain and keeping physical fitness:

     Don't skip meals. Before you leave home, have a small, low-fat meal or snack. This may help to

avoid getting too excited before delicious foods.

     Control portions. Use a small plate (about 10 inches) and put aside the large ones that may

encourage you to "load up." You should be most comfortable eating an amount of food about the size

of your fist. Once you have your "tasting" serving, move away from the buffet. Doing so will make it less

tempting(诱惑) to be eating constantly(持续不断的) as your appetite (胃口) is inspired by the sight of

food.

     Begin with soup and fruit or vegetables. Fill up beforehand on water-based soup and raw fruit or

vegetables. Or drink a large glass of water before you eat to help you feel full.

     Stick to physical activity. Don't let exercise take a break during the holidays. A 20-minute walk

after a meal can help burn off extra calories.

     Avoid high-fat foods. Dishes that look oily or creamy may have a large amount of fat. Choose lean

meats. Fill your plate with salad and green vegetables. Use lemon juice instead of dressing or butter.

1. Which of the following is WRONG according to the passage?

A. You had better turn your attention away from delicious foods.

B. Drinking some water of soup before eating helps you eat less.

C. Holidays are happy days with pleasure but they may bring weight problems.

D. Physical exercise can reduce the chance of putting on weight

2. Many people can't control their weight after the holidays mainly because they______.

A. can't help being tempted to eat constantly  

B. take part in too many parties

C. enjoy delicious foods      

D. can't help turning away from the foods

3. If the passage appears in the newspaper, you think it should be ______ Column.

A. Holidays and Festivals

B. Health and Fitness

C. Fashion and Frontier

D. Student Times Club

4. The best title for the passage would probably be ______.

A. How to avoid holiday feasting and celebrating

B. Dos and Don'ts for keeping slim and fit

C. How to avoid weight gain over holidays

D. Wonderful holiday, Boring weight