A professor of statistics assumes that the marks in his course are normally distributed. He did calculations and found that his morning classes average 73% with a standard deviation of 12% on their final exams. His afternoon classes average 77% with a standard deviation of 10%. What is the probability that the mean mark of a random sample of four students from a morning class is greater than the average mark of a random sample of four students from an afternoon class?

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’n Professor in statistiek neem aan dat die punte vir sy kursus normaal verdeel is. Hy doen berekenings en vind dat sy oggendklasse ʼn gemiddeld van 73% met ʼn standaardafwyking van 12% vir hulle finale eksamen behaal het. Sy middagklasse het ʼn gemiddeld van 77% met ʼn standaardafwyking van 10% vir hulle finale eksamen behaal. Wat is die waarskynlikheid dat die gemiddelde punt van ʼn steekproef van vier ewekansige studente uit die oggendklasse hoër is as die gemiddelde punt van ʼn steekproef van vier ewekansige studente uit die middagklasse?