1. A manufacturer of light bulbs produced bulbs for which the lines are normally distributed with a mean of 1500 hours and a standard deviation of 250 hours. If the manufacturer decides he wants only 2.5% of the bulbs to have a life less than his guaranteed number of hours, what number must he choose for his guarantee?

2. When a sample of 200 hen egg is graded, there is a mean weight of 41g. if the standard deviation of the weight of hen egg is known to be 4g, find a 95% confidence interval for the mean weight.

3. Determine the minimum sample size required to estimate average weight of Foundation Studies boys to within 1.0kg with 98% confidence. Assume that the standard deviation of such weights is 3.0kg