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- This topic has 5 replies, 2 voices, and was last updated 7 months, 1 week ago by John Moffat.

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- September 22, 2019 at 1:43 pm

ivie2019ParticipantThe results of an accountancy exam are normally distributed with a mean score of 58 and standard deviation of 10.

what is the percentage probability that a student will score more than 80 (to 2 decimal places)?___%

Dear John, can you please tell me how to do these kind of questions ?

thank you!!!September 22, 2019 at 3:18 pm

John MoffatKeymasterThe distance between 80 and the mean of 58 is 22, which is 22/10 or 2.2 standard deviations (and is the z-score).

From the normal distribution tables, the probability of being between 58 and 80 is therefore 0.4861.

Because of symmetry, the probability of being above the mean of 58 is 0.5.

Therefore the probability of being more than 80 is 0.5 – 0.4861 = 0.0139 (or 1.39%)

Using the normal distribution is all dealt with in my free notes and the free lectures that work through and explain the notes.

September 29, 2019 at 9:43 pm

ivie2019ParticipantHi! I didn’t understand anything and gone through lecture notes as well…

September 30, 2019 at 8:03 am

John MoffatKeymasterBut did you watch the lectures? It is completely pointless to use our lecture notes without watching the free lectures that work through them.

October 17, 2019 at 10:10 pm

ivie2019ParticipantI don’t understand from where did 0.5 came from?

I just had another mock test with again two questions which are almost identical to this one just different numbers…

I really have no idea :/October 18, 2019 at 7:51 am

John MoffatKeymasterThe normal distribution is symmetrical about the mean. There is therefore a 0.5 (50%) chance of being either above or below the mean.

I ask again – have you actually watched my free lectures where all this is explained in detail? You cannot expect me to type out all of my lectures here 🙂

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