Unit Test — Unit test Answers

A credit card company is interested in the proportion of its customers who pay their minimum balance on time. The company randomly sampled 500 records from the previous month. The 95% confidence interval for the true proportion of customers who pay on time was (0.765, 0.835). What are the point estimate and the margin of error for this interval?

A computer company wants to determine if there is a difference in the proportion of defective computer chips in a day’s production from two different production plants, A and B. A quality control specialist takes a random sample of 100 chips from the first hour of production from plant A and determines that there are 12 defective chips. The specialist then takes a random sample of 100 chips from the last hour of production from plant B and determines that there are 10 defective chips. Assuming conditions for inference are met, what is the 90% confidence interval for the true difference in proportions of defective chips from a day’s production between the two plants? Find the z-table here.

A local school board wants to determine the proportion of households in the district that would support starting the school year a week earlier. They ask a random sample of 100 households whether they would support starting the school year a week earlier, and 43 households responded that they would. The school board plans to construct a 95% confidence interval for the true proportion of households that would support starting the school year a week earlier. Are the conditions for inference met?

A student believes that a certain number cube is unfair and is more likely to land with a six facing up. The student rolls the number cube 45 times and the cube lands with a six facing up 12 times. Assuming the conditions for inference have been met, what is the 99% confidence interval for the true proportion of times the number cube would land with a six facing up?

A newspaper poll found that 54% of the respondents in a random sample of voters in the city plan to vote for candidate Roberts. A 95 percent confidence interval for the population proportion is 0.54 ± 0.06. Based on this interval, what can the newspaper report?