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2) 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?Answer = Z = (x – µ)/?
2.28 = (90-70)/?
0.4887 = 20/?
? = 20/0.4887
? = 40.92Mr Moffat can you please tell me if my answer is correct and can you please help me correct it if its wrong, i found this in the ACCA practice test and we’re not given the answers for it. Thanks a lot Mr Moffat, May god bless you.
Your answer is calculating as though they are scoring between 70 and 90, but the questions asks for more than 90.
(The ACCA does give answers to the practice tests).
Given that there is a 2.28% chance of being more than 90, there is a 47.72% chance of being between 70 and 90.
Working backwards in the tables, to get 0.4774 is 2 standard deviations.
Therefore 1 standard deviation is (90-70)/2 = 10
Have you watched my free lectures on this?
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