
zscores?
hi there,
could anyone help me out? i really don't understand zscores... i have a final coming up and i can't contact my teachers because they are all on holidays.
for a given question, do i use the formula: z=(xmean)/(standard deviation)? because when i am given the values for x, the mean, and standard deviation to find z, i always end up with a negative number or something that doesn't seem right. For example,
x= 20
Mean = 45
Standard Deviation = 12
How do I find the zscore using these values? It can't be just plugging the values into the formula. How do I use the chart? As well, what if I am not given an x values? What do I do?
thanks.

It is true that you simply plug these values into the formula above.
$\displaystyle z = \frac{X\mu}{\sigma} = \frac{2045}{12} = 2.08$
Now do you need to only find the zscore? Sometimes we need to find the probability of z being greater or less than this score.

yes. how do i find the probability, whether it is greater than or less than the zscore?

You need to use a table/chart, this online calculator is handy.
Z table  Normal Distribution