The internal evaluation for Economics course in an Engineering programme is based on the score of four quizzes. Rahul has secured 70, 90 and 80 in the first three quizzes. The fourth quiz has ten True-False type questions, each carrying 10 marks. What is the probability that Rahul’s average internal marks for the Economics course is more than 80, given that he decides to guess randomly on the final quiz?
Explanation:
Average marks of the first three quizzes = 80
So, for Rahul to have average internal marks more than 80, he has to score more than 80 marks in the last quiz.
This is possible if he attempts 10 questions or 9 questions correctly.
Number of ways this can be done = 1 + 10C9 = 1 + 10 = 11
Total number of ways the quiz can be solved = 210 = 1024
∴ The required probability = 11/1024
Hence, option (b).
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