Hi sir, Please explain this questions. Q1)A normal distribution has a mean of 75and a variance of 25. what is the upper quartile of this distribution? Q2)A normal distribution has mean of 150,and a standard deviation of 20. 80% of the distribution is below which of the following (approximately)?

In future please ask this kind of question in the Ask the Tutor forum, and not as a comment on a lecture.

For the first question you need to find the value that has a probability of 25% (0.25) of being above the mean. For the second question you need to find the value that has a probability of 80 – 50 = 30% (0.30) below the mean.

In both cases you need to work backwards in the tables to find the number of standard deviations (the z score) in the way I explain in the lectures.

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faizalcs says

Hi sir,

Please explain this questions.

Q1)A normal distribution has a mean of 75and a variance of 25.

what is the upper quartile of this distribution?

Q2)A normal distribution has mean of 150,and a standard deviation of 20.

80% of the distribution is below which of the following (approximately)?

John Moffat says

In future please ask this kind of question in the Ask the Tutor forum, and not as a comment on a lecture.

For the first question you need to find the value that has a probability of 25% (0.25) of being above the mean.

For the second question you need to find the value that has a probability of 80 – 50 = 30% (0.30) below the mean.

In both cases you need to work backwards in the tables to find the number of standard deviations (the z score) in the way I explain in the lectures.

iza1 says

what if the z score for 10 and 10.4 is 2. 96

then the area from curve table that we would choose is 2.906 ‘s = 0 .4985 ?

iza1 says

Hi SIr,

Can you please explain again what you meant by area of bar is proportional to frequency.

I cant seem to understand it