1. Calls arrive at a switchboard a mean of one every 30 seconds. If call arrivals follow the exponential distribution, find the 80th percentile for the time between call arrivals.
2. The weight of trucks traveling on a particular section of I-475 has a population mean of 15.8 tons and a population standard deviation of 5.2 tons. What is the probability a state highway inspector could select a sample of 50 trucks and find the sample mean to be 14.3 tons or less?
3. The wildlife department has been feeding a special food to rainbow trout fingerlings in a pond. Based on a large number of observations, the distribution of trout weights is normally distributed with a mean of 402.7 grams and a standard deviation of 8.8 grams. What is the probability that the mean weight for a sample of 43 trout exceeds 405.5 grams?
4. Suppose a research firm conducted a survey to determine the mean amount steady smokers spend on cigarettes during a week. A sample of 110 steady smokers revealed that the sample mean is $20. The population standard deviation is $5. What is the probability that a sample of 110 steady smokers spend between $19 and $21?
5. According to the central limit theorem, ______.

• the sampling distribution of the sample means will be skewed
• the population mean and the mean of all sample means are equal
• increasing sample size decreases the dispersion of the sampling distribution
• the sampling distribution of the sample means is approximately normally distributed