The normal probability curve and stem-to-leaf diagram of the data are shown in figure; $\sigma$is known.

Perform Hypothesis test for mean of the population from which data is obtained and decide whether to use z-test, t-test or neither. Explain your answer.

Small Sample size:

For sample size less than 15, the z-test procedure is used when the variable is normally distributed or very close to being normally distributed.

Moderate Sample size:

For sample size between 15 and 30, the z- test procedure is used when the variable is far from being normally distributed or outlier is absent in the data.

Large Sample size:

For sample size greater than 30, the z- test procedure is used without any restriction.

Small Sample size:

• Samples are randomly selected from the population.

• Population follows normal distribution or the sample size is larger.
• The standard deviation is unknown.

Here, the sample is selected from the population and the sample size is small. Moreover, the distribution of the variable is not normally distributed. Hence, neither test is used for given scenario.