Warm up: AMC-1-8-20

A survey should always be ____ and ____.

• random and biased

• random and unbiased

At an assembly 7 out of 10 students who entered the gym were carrying a backpack. Based on this information, if 700 students were at the assembly, how many students could be expected to be carrying a backpack?

• 49

• 490

• 210

• 421

Ana wants to know the average student’s opinion of the tardy policy at her school. Which group of students should she survey in order to achieve the most accurate results?

• thirty students who are often tardy

• thirty students who are rarely tardy

• thirty of her friends

• thirty randomly selected students from her school

A sample should be

• representative of only people from middle income

• a very large group

• representative of the population

• representative of people who volunteer

The Student Council asked every tenth student in the lunch line how they preferred to be contacted with school news. The results for every student contacted are shown in the table. Is this an unbiased sample? If yes, suppose there are 684 students at the school. How many can be expected to prefer E-mail?

• No, it's a biased sample

• 432

• 304

• 16

A radio station asks its listeners to dial one of two numbers to indicate their preference for one of two candidates in an upcoming election. Of the responses received, 76% favored candidate A. If there are 1,500 registered voters, how many will vote for candidate A?

• 1,140

• 6

• 1,974

• 100

To determine the number of umbrellas the average household in the United States owns, a survey of 100 randomly selected households in Arizona is conducted. Of the households, 24 said that they own 3 or more umbrellas. The researcher concluded that 24% of the households in the United States own 3 or more umbrellas. Is this a valid conclusion? Justify your answer.

• Valid. The sample is biased.

• Not valid. The sample is biased.

• Valid. The sample is unbiased.

• Not valid. The sample is unbiased.

A company makes DVDs and randomly selects 25 from 1500 to test them to see if they work.

• Biased

• Unbiased