a random sample of 20 items is selected from a population. to determine the appropriate critical t-value what number of degrees of freedom should be used? a. 20 b. 19 c. 21 d. 25


  1. T value comes when n is less than 30, when we do not know the value of population standard deviation.
    In this case, the degree of freedom is sample – 1, so 20-1 = 19, option b


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