Estimation using Normal Distribution

A random sample of 55 adults in a certain country showed an average height of six feet (72 inches) for adults. Statistics show the population standard deviation to be 3.40 inches. Calculate the 95% confidence interval for the mean height of the adult population.

Estimation using Normal distribution

In the last municipal election, a sample of 350 registered voters showed that 85 voted for the incumbants. Find a 98% confidence interval estimate for the proportion of all voters voting for the incumbants.

Estimation: confidence interval for the difference of proportions. Develop a 90% confidence interval for the difference of proportions who answered "yes".

After a certain candidate announced his intention for running for the premiership of a province, many polls were conducted to assess his chanced for success. Among them were two polls of independant samples taken from two populations. The poll in the first community interviewed 400 people and asked if the candidate had a chance of becoming the next premier. Out of this sample of 400, 192 people responded "yes". In the second community, 300 people were asked exactly the same question, and 108 answered "yes". Develop a 90% confidence interval for the difference of proportions who answered "yes".

Estimation is examined.

"Hockey-r-us," a store specializing in sales of hockey equipment, wants to find out the average age of all its customers. A random sample of 25 customers reveals an average age of 38 years with a standard deviation of six years. It determines a 95% confidence interval of the average age of all customers.

Estimation

In an election campaign, the party vying for an upset polls a sample of 100 voters. The party finds that 60 of 100 clearly express the intention of voting in favor of the party polling. How many voters should be sampled if the party wants to estimate the population proportion with a sampling error of 5% or less? (Use confidence level of 95%)