A placement exam is given to 36 randomly chosen college students. Their mean score is 63.6 with the standard deviation of 15.1 points. Develop a 90% confidence interval for mean score on this placement exam for all students.
a. 23.48 < = mean <= 27.32
b. 2.42 <= mean <=3.98
c. 59.46 < = mean < = 67.74
d. 17.70 < = mean < = 18.90