Ndtyjky

I am stuck in a statistics assignment, and would really appreciate some qualified help.

We have been given a data set and are then asked to find the 10% with the lowest rate of profit, in order to decide what Profit rate is the maximum in order to be considered for a program.

the data has:
Mean = 3,61
St. dev. = 8,38

I am thinking that i need to find the 10th percentile, and if i run the percentile function in excel it returns -4,71.

However I tried to run the numbers by hand using the z-score.

where z = -1,28

z=(x-μ)/σ

Solving for x

x= μ + z σ



x=3,61+(-1,28*8,38)=-7,116

My question is which of the two methods is the right one? if any at all.

I am thoroughly confused at this point, hope someone has the time to help.

Thank you

This is the assignment btw:

"The Danish government introduces a program for economic growth and will
help the 10 percent of the rms with the lowest rate of prot. What rate
of prot is the maximum in order to be considered for the program given
the mean and standard deviation found above and assuming that the data
is normally distributed?"

The excel formula is giving the actual, empirical 10th percentile value of your sample

If the data you have includes all possible instances of whatever you’re trying to measure, then go ahead and use that.

If you’re sampling from a population and your sample size is small, use a t distribution or increase your sample size. If your sample size is healthy and your data are normally distributed, use z scores.

Short story is the different outcomes suggest the data you’ve supplied are not normally distributed.