Based on the information compute the confidence interval using the t-distribution
1. A tire manufacturer wishes to investigate the tread life of its tires. A sample of 20 tires driven 60,000 miles revealed a sample mean of .28 inch of tread remaining with a standard deviation of 0.08. Construct a 95% confidence interval.
2. A consumer group would like to estimate the mean monthly electricity charge for a single family house in July within $5 using a 99% level of confidence. Based on similar studies the standard deviation is estimated to be $20. How large a sample is required?
3.The American Kennel Club wanted to estimate the proportion of children that have a dog as a pet. If the club wanted the estimate to be within 3% of the population proportion, how many children would they need to contact? Assume a 95% level of confidence and that the club estimated that 30% of the children have a dog as a pet.
Show your work please.