Chapter 18 Quiz

A certain population is strongly skewed to the right. We want to estimate its mean, so we will

collect a sample. Which should be true if we use a large sample rather than a small one?

• A) I only

• B) II only

• C) III only

• D) II and III only

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CCSS.6.SP.A.2

A certain population is strongly skewed to the left. We want to estimate its mean, so we collect

a sample. Which should be true if we use a large sample rather than a small one?

• A) I only

• B) II only

• C) III only

• D) I and III only

Tags

CCSS.6.SP.A.2

Which is true about the sampling distribution of a statistic with sample size n?

• A) I only

• B) II only

• C) III only

• D) II and III

Which of the following is true about Student’s t-models?

• A) I only

• B)I and II

• C) I and III

• D) I, II, III

A marketing company reviewing the length of television commercials monitored a random

sample of commercials over several days. They found that a 95% confidence interval for the

mean length (in seconds) of commercials aired daily was (23, 27). Which is true?

• A) 95% of the commercials they checked were between 23 and 27 seconds long.

• B) Commercials average between 23 and 27 seconds long on 95% of the days.

• C) 95% of all samples would show mean commercial length between 23 and 27 seconds.

• D) We’re 95% sure that the mean commercial length is between 23 and 27 seconds.

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CCSS.HSS.IC.B.4

A coffee house owner knows that customers pour different amounts of coffee into their cups. She samples cups from 10 costumers she believes to be representative of the customers and weighs the cups, finding a mean of 12.5 ounces and standard deviation of 0.5 ounces. Assuming these cups of coffee can be considered a random sample of all cups of coffee which of the following formulas gives a 95% confidence interval for the mean weight of all cups of coffee?

• 
• 
• 
• 

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CCSS.HSS.IC.B.4

An elementary school principal wants to know the mean number of children in families whose children attend this school. He checks all the families using the school’s registration records, and we use the computer to create a 95% confidence interval based on a t-distribution. This procedure was not appropriate. Why?

• A) Since these families are from only one school, the family sizes may be skewed.

• B) The entire population of families was gathered so there is no reason to do inference.

• C) The recent record-setting family with twelve children is probably an outlier.

• D) At a given school families are not randomly selected.

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CCSS.HSS.IC.B.4

Trainers need to estimate the level of fat in athletes to ensure good health. Initial tests were based on a small sample but now the trainers double the sample size for a follow-up test. The main purpose of the larger sample is to...

• A) reduce bias.

• B) decrease the variability in the population.

• C) decrease the standard deviation of the sampling model.

• D) reduce confounding due to other variables.

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CCSS.HSS.IC.B.4

An ecologist who analyzes water samples tests the null hypothesis that any contaminants in the water are below dangerous concentrations. Because he uses alpha = 0.05, a set of samples from a small lake that produced a P-value of 0.07 led him to conclude that the evidence did not point to unsafe water conditions. Which is true?

• A) There’s a 7% chance the lake’s water really is safe.

• B) There’s a 93% chance the lake’s water really is safe.

• C) There’s a 7% chance his sampling would have shown as much contamination as it did even if the lake’s water really is safe.

• D) If the lake’s water really is unsafe, there’s a 5% chance he wouldn’t notice.

• E) If he had taken more samples, he probably would have rejected the null and concluded that the water was unsafe.

Maria has data from a random sample of 16 subjects and is constructing a 95% confidence interval for the population mean. Which value should she use for t*?

• A) 1.753

• B) 1.960

• C) 2.120

• D) 2.131

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CCSS.HSS.IC.B.4