Question

When constructing a confidence interval the Z stand normal distribution is used when
1. The sample is given (n>30)
2. The sample variance is given
3. The population variance is given
4. The question is to calculate the 9% confidence interval
5. The level of significance is 1% , 5% or 10%

Answer 1

Z is used when the population standard deviation(square root of population variance) is known and the data is normally distributed irrespective of the size(n). If the distribution is normal but population standard deviation is unknown, t-distribution is used.

Thus, option 3 is correct.