Question

Use a table to find a z-score that fits the given conditions. Interpolate if necessary.

10% of the area under the standard normal curve is above the score. Can anyone explain how to do this? I'm lost.

Answer 1

sounds like you want to find the value of k such that

P(Z > k) = 0.10

Answer 2

are you allowed to use a calculator?

Answer 3

yes

Answer 4

yes, I am.

Answer 5

ok one calculator you can use is wolfram alpha

you would use the normalcdf function to get this

http://www.wolframalpha.com/input/?i=normalcdf&a=*C.normalcdf-_*Formula.dflt-&f2=0.10&x=0&y=0&f=NormalProbabilities.pr_0.10&a=*FVarOpt.1-_***NormalProbabilities.pr--.***NormalProbabilities.z--.**NormalProbabilities.l-.*NormalProbabilities.r---.*--&a=*FVarOpt.2-_**-.***NormalProbabilities.mu--.**NormalProbabilities.sigma---.**NormalProbabilities.pr---


notice how there is a line on that page that says P(Z > 1.282) = 0.1

so k = 1.282 is the value we're looking for

Answer 6

Okay that makes sense. I am still a little confused how you figured out how 0.1 = 1.282

Answer 7

they aren't equal like that

Answer 8

its more like

P(Z > 1.282) = 0.10

Answer 9

in other words

the probability of picking a z-score larger than 1.282 is 0.10 (or 10%)

Answer 10

okay so lets say another question asks 33% of the area under the standard normal curve is above the score. Then would the answer be -.44 ?

Answer 11

on that calculator page, you now type in 0.33

Answer 12

then you look for the line that has P(Z > ???) = 0.33

Answer 13

okay so it is 0.44 not negative

Answer 14

yep

P(Z > 0.44) = 0.33

Answer 15

Thank you for your help ! :)

Answer 16

you're welcome