Which of the following statements is NOT true?

A researcher is interested in whether a certain medication has an effect on memory capacity. The researcher obtains a sample of n = 250 participants and give each participant a certain amount of the medication. After a year, the participants had their memory capacity measured. The mean memory capacity of the sample is equal to M = 62 with s = 18. The average memory capacity is mu equal to 55. Based on the sample, did the medication have a significant effect on memory capacity? Use a significance level of 5%. Which of the following is NOT true? The positive critical value is equal to 1.646. The positive critical value is equal to 1.984. The negative critical value is equal to -1.984. O The degree of freedom used on its corresponding table is 100