Supposexhas a normal distribution withs=1.8. A random sample of size19has a sample mean ofx= 50.

(a) What conditions are necessary for your calculations? (Select all that apply.)

• normal distribution ofx
• is known
• is unknown
• uniform distribution ofx

(b) Find a 90% confidence interval for mu. What is the margin of error? (Round your answers to two decimal places.)

• lower limit =
• upper limit =
• margin of error=

(c) Interpret your results in the context of this problem.

• 1. The probability that this interval contains the true average is 0.80.
• 2. There is a 90% chance that the interval is one of the intervals containing the true average.
• 3. There is a 20% chance that the interval is one of the intervals containing the true average.
• 4. The probability that this interval contains the true average is 0.20.