1. According to Fortune, solar power now accounts for only 1% of total energy produced.15 If this number was obtained based on a random sample of 8,000 electricity users, give a 95% con?dence interval for the proportion of users of solar energy.
2. Money magazine is on a search for the indestructible suitcase.16 If in a test of the Helium Fusion Expandable Suiter, 85 suitcases out of a sample of 100 randomly tested survived rough handling at the airport, give a 90% con?dence interval for the population proportion of suitcases of this kind that would survive rough handling.
3. A machine produces safety devices for use in helicopters. A quality-control engineer regularly checks samples of the devices produced by the machine, and if too many of the devices are defective, the production process is stopped and the machine is readjusted. If a random sample of 52 devices yields 8 defectives, give a 98% con?dence interval for the proportion of defective devices made by this machine.
4. Before launching its Buyers' Assurance Program, American Express wanted to estimate the proportion of cardholders who would be interested in this automatic insurance coverage plan. A random sample of 250 American Express cardholders was selected and sent questionnaires. The results were that 121 people in the sample expressed interest in the plan. Give a 99% con?dence interval for the proportion of all interested American Express cardholders.