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a. A student has grades of 84, 65, and 76 in three courses. What grade must he obtain on the next course to have an average of exactly 80 for the four courses?

b. A mean score of 80 is needed for awarding final grade B in five examinations. Ahmad's first four examination grades are 72, 74, 85, and 81. What grade does Ahmad need in the fifth examination for achieving B in the course?

 c. A student has scored 88% in home assignments, 97% in midterm examination and 98% in the final examination of probability and statistics course. If the respective points are 25, 25 and 50, what then is the overall percentage of the student in the course?

d. Five group of students that consist of 10, 8, 11, 13 and 9 individuals. They consumed the mean average time in computer programming were 18, 33, 11, 42 and 53 hours respectively. Find the overall average time consuming the student groups in computer programming.