a. Mean score on a Math test is 80, with a standard deviation of 10. Between what two scores must this mean lie to represent 8/9 of the data set.

b. The marks obtained by a set of students in an examination are given below: Marks 5 10 15 20 25 30 Number of Students 6 4 6 12 x 4 Given that the mean mark of the set is 18, calculate the numerical value of x.

c. Calculate the percentile of 85, in the given data set { 76,98,85,80,83,84}