Help with Z-Scores in Excel (Normal Distribution)

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zachj06

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Jan 31, 2015
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Hello I am having trouble with a specific problem involving Z-Scores in Excel.

I know the answer to this question:
"10% of the values of a standard normal distribution are less than z. Find the Z Score."

This would be Z = -1.281551566. I computed this in Excel doing: =NORMSINV(10%).

The question I am having trouble with is:
"10% of the values of a standard normal distribution are greater than or equal to z."

I think all I do is =1 - NORMSINV(10%). This gives me Z = 2.281551566. Is this correct? It just doesn't seem correct to me.

I think the answer may be 1.281551566

Thank you for your help, please let me know if there is anything I need to clarify.
 
Last edited:
zachj06 said:
Hello I am having trouble with a specific problem involving Z-Scores in Excel.

I know the answer to this question:
"10% of the values of a standard normal distribution are less than z. Find the Z Score."

This would be Z = -1.281551566. I computed this in Excel doing: =NORMSINV(10%).

The question I am having trouble with is:
"10% of the values of a standard normal distribution are greater than or equal to z."

I think all I do is =1 - NORMSINV(10%). This gives me Z = 2.281551566. Is this correct? It just doesn't seem correct to me.

I think the answer may be 1.281551566

Thank you for your help, please let me know if there is anything I need to clarify.
Click to expand...

The interpretation of the first statement is, I believe,
P(z < z0) = 0.1
find z0.

For the second question, the formula you used is for proabability, not the values of the population (the z0's). So it should be NORMSINV(100% - 10%) or NORMSINV(1 - .1) which would be
P(z<z1) = 0.9
find z1.
 
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