The marks of students in a course is normally distributed with mean 64 and standard deviation of 12. The lecturer wishes to set the distribution of grades for this course as follows: Grade %age of students to Cut-off marks achieve the grade 3% 20% 65% 10% 2% QB'Q 'I'IUncnb a) Determine the 1St and 3rd quartile values for this distribution. (4m) b) Determine the values of the cutoff marks (a, b, c, d) (10m) (e.g. Cut-off mark a = the minimum mark to achieve the grade A)