Question

what proportion of a normal distribution falls between z=-.65 and z=+.65?

Answer 1

look up the probability to the left of z=.65, and subtract the probability to the left of z=-.65.

Answer 2

have you used a standard normal chart?

Answer 3

yes but its confusing its my first time and i dont know where to start

Answer 4

it is symmetric so you can also find 1-2* P(z<-.65)

Answer 5

ok let me find a chart online and ill help you

Answer 6

thank you so much

Answer 7

http://www.stat.ucla.edu/~ywu/teaching/normal.pdf

Answer 8

that's a good one, go there and let me know if the link works

Answer 9

the link wont work for some reason

Answer 10

ok let me see if I can find a similar one

Answer 11

http://www.sjsu.edu/faculty/gerstman/EpiInfo/z-table.htm

Answer 12

that's only a partial table but you can get the basic idea

Answer 13

does it work?

Answer 14

yes it works so do i look up -,65
and .65

Answer 15

you would if it was a full table but we only have positive values here so we have to do some more work

Answer 16

you can start by looking up .65

Answer 17

the tenths place is in the first column, so go to .6

Answer 18

ok so i see .6

Answer 19

as you move over to the right you are adding one to the hundreths place. you can see the hundreths place an the top row of the chart

Answer 20

0.7422

Answer 21

look for .05, and find where the row .6 meets the column .05, that is the probability to the left of .65

Answer 22

yep that's right.

Answer 23

now we need to subtract P(z<-.65)

Answer 24

standard normal is symmetric so P(z<-.65)=P(z>.65)

Answer 25

so how would we find the negative

Answer 26

P(z>.65)=1-P(z<.65)=1-.7422=.2578

Answer 27

so P(z<.65)=.7422
P(z<-.65)=.2578
and we subtract them to find the probability in between

.7422-.2578=.4844

Answer 28

if you had a full table you could have just looked up z=-.65

Answer 29

thanls so much, i really understand that now

Answer 30

great glad it helped :)

Answer 31

cya

Answer 32

bye:)