1. The standard error of the mean for a sample of 100 is 40. In order to cut the standard error of the mean to 20, we would change the sample size to _________

2. A company that sells annuities must base the annual payout on the probability distribution of the length of life of the participants in the plan. Suppose the probability distribution of the lifetimes of the participants is approximately a normal distribution with a mean of 68 years and a standard deviation of 3.5 years. What percentage of the plan recipients would receive payments beyond age 75?

3. A major department store chain is interested in estimating the average amount its credit card customers spent on their first visit to the chain's new store in the mall. Fifteen credit card accounts were randomly sampled and analyzed with the following results: X-bar = $50.50 and s2 = 400. Construct a 95% confidence interval for the average amount its credit card customers spent on their first visit to the chain's new store in the mall.