Question

PLEASE....Nicole missed the lesson on normal distribution and needs to do her homework. Explain to Nicole how to use the mean and standard deviation of a normal distribution to determine the top 5% of the population.

Answer 1

does the nichole, or the person explaining to her ... know what a z score is?

Answer 2

some texts call it a "standard" score

Answer 3

Well I have this down in my asnwer box... "Using the Z chart I have to find the number for 0.05 which is .95053 and slide over to get 1.6. So it becomes 1.65. "

Answer 4

thts almost coherent, but lacks a little

Answer 5

what do we use the Zchart for? and how do we use it?

Answer 6

We use the Z chart for idk

Answer 7

then your explanation doesnt mean anything ...

Answer 8

can you tell me what a zchart looks like?

Answer 9

Well I know that we need it for this formula x=x-mean/sigma

Answer 10

it would be nice to know and have i agree, and this question assumes that your lessons have covered it and is assessing your understanding of it.

Answer 11

I have it printed it has 0.0-3.9 on the left side and at the top it has .00-.09 and there is numbers throughout it

Answer 12

the top and left sides are the zscore, split up

say z = 2.35

row 2.3 and col .05 cross in the middle at some .xxxx value

what is the value related to z=1.26?

Answer 13

..89617

Answer 14

good, then we know how to read it ... 8962 is what i see in mine

Answer 15

now, look in the middle for a number that is close to .9500 we are going to work the table from the inside out

Answer 16

1.65 which is what I said

Answer 17

the value is .95053

Answer 18

1.65 is fair, but ... notice that 1.64 and 1.65 and .9500 exactly in the middle

so we would want to use the average of them. i think thats the only one that happens on.

but either way, 1.65 is fair for this

Answer 19

you did not explain very well how we get the z score, which is why we covered this

Answer 20

Using the Zchart, find the field value closest to .9500 (why?) becuase our top 5% is a right tail and we are using a left tail chart. left tail value is 1 - .05 = .95

now work the z formula backwards

z = (x-mean)/sd

solve for x since everything else is known

Answer 21

How is the mean and standard deviation known?

Answer 22

.... they are stated in the information inthe problem of course

Answer 23

or at least they were the last time i worked this thing

Answer 24

I didnt mean that

Answer 25

at any rate, if we know the mean and sd, plug them in to determine the value of x

z = (x-mean)/(sd)

how do we solve for x?

Answer 26

1.65=(x-mean)/(sd)

I dont know actually

Answer 27

its a basic algebra problem now .... how do we solve for an unknown? we get it all by itslef on one side

Answer 28

multiply

Answer 29

good

1.65(sd) = x - mean

then ...

Answer 30

subtract x from mean and cancel it out?

Answer 31

um, add the mean to both sides to get x all alone

1.65(sd) + mean = x - mean + mean

1.65(sd) + mean = x

Answer 32

oh yeah my bad

Answer 33

Okay totally makes sense

Answer 34

:) good luck

Answer 35

most of the other people in here didnt know what or how to find a zscore; which of course makes the problem way more difficult then it has to be.

Answer 36

Okay thank you, if I open another question will you help me with it?

Answer 37

im going to be preoccupied, but theres plentyon here that are good at this stuff. theyll repsond.

Answer 38

they may even be able to type better

Answer 39

Ok thanks again!!!