A significance test is to be conducted concerning population means and based on the difference between the two sample means . What assumptions are required in order for the two-sample z statistic to be valid

In order for the two-sample z statistic to be valid we need that the following assumptions hold:

each sample and population must be independent from each othereach population must be normally distributedthe population standard deviations must be known or the sample sizes must be ≥ 30samples must be randomdata has to be continuous