Preparing to Estimate a Population Proportion Answers

A computer company wants to determine the proportion of defective computer chips from a day’s production. A quality control specialist takes a sample of 100 chips from the first hour of production and determines that there are 12 defective chips. He wants to construct a 90% confidence interval for the true proportion of defective chips from a day’s production. 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?

In a small town of 5,832 people, the mayor wants to determine the proportion of voters who would support an increase to the food tax. An assistant to the mayor decides to survey 1,000 randomly chosen people to construct a 90% confidence interval for the true proportion of people who would support the increase in food tax. Of the sample, 363 people say they would support the increase. Are the conditions for inference met?

After a hailstorm, a large car dealership wants to determine the proportion of cars that have damage. The service department randomly selects 50 cars on the dealership lot, examines them, and determines that 18 have damage. Assuming all conditions have been met, they construct a 99% confidence interval for the true proportion of cars with damage from the storm. What are the calculations for this interval?

What is the z* critical value for constructing a 90% confidence interval for a proportion?Find the z-table here.

What is the z* critical value for constructing a 94% confidence interval for a proportion?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 statistics student wants to survey a high school of 910 students concerning support for increasing the number of student parking spots. The student randomly selects 90 students, and finds that 63 support increasing the number of student parking spots. Assuming the conditions for inference have been met, what is the 95% confidence interval for the true proportion of students who would support the increase in the number of parking spots?

What is the z* critical value for constructing a 99% confidence interval for a proportion?Find the z-table here.

A teacher has a large container of blue, red, and green beads. She wants her students to estimate the proportion of red beads. Each student selects 50 beads, counts the number of red beads, and returns the beads to the container. One student sample has 15 red beads. The students are asked to construct a 95% confidence interval for the true proportion of red beads in the container. Are the conditions for inference met?