MHB Mean & Std Dev for Norm Dist. Exam Marks - 450 Stud.

wajeehayas
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Assuming that the number of marks scored by a candidate is normally distributed, find the mean and the standard deviation, if the number of first class students(60% or more marks) is 25, the number of failed students(less than 30%marks) is 90 and the total number of candidates appearing for the examination is 450.
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