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The percentage probability that a student will score more than 90 marks in an accounting exam is 2.28%. the marks scored from the accounting exam follow a standard normal distribution with a mean mark of 70. What is the standard deviation for the distribution?
Can you please explain how do i apply the formula here?
Do not simply learn formula – the questions in the exam are deliberately designed to check that you understand rather than have just learned formulas.
Because of symmetry, the proportion between the mean and 90 is 0.5 – 0.028 = 0.472.
Use the tables ‘backwards’, as I explain in the free lectures, to determine how many standard deviations give 0.472 as the results.
The distance between the mean and 90 is 20. So divide 20 by the figure you get from the tables, and that is the standard deviation required by the question 🙂
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