Question

Assume the readings on thermometers are normally distributed with a mean of 0C and a standard deviation of 1.00C. Find the probability that a randomly selected thermometer reads between -2.24 and -1.38.
The probability is =

Answer 1

and your thoughts?

Answer 2

we are given a low value, a high value, a mean, and a deviation

what function have we used that has these for inputs?

Answer 3

By trying to find the area to the left of z?

Answer 4

INVNORM?

Answer 5

we have covered this before, its may be useful to make notes ....

Answer 6

I agree ugh sorry

Answer 7

how do we find the area between high and low values?

the inverse of this operation defines a z score, we already have z scores so the invnorm function isnt going to be useful to us.

Answer 8

normalcdf?

Answer 9

thats the one

and how do we input the information?

Answer 10

Annnd thats what I forgot :(

Answer 11

try to recall, what would you say is the most reasonable ?

Answer 12

normalcdf(-1.38,-2.24,0,1)

Answer 13

good effort, 0,1 is in the right spots

but low,high is off

-2.24 is to the left of -1.38, since its less than -1.38

Answer 14

inputs are in order: low, high, mean, deviation

Answer 15

you can try it as high, low .. it might say you did an error tho :)

Answer 16

Ok, I'll try now

Answer 17

the wolf takes the syntax: P((-2.24-0)/1 <z< (-1.38-0/1)), for a mean of 0 and sd of 1

just in case we need a reference to compare with

Answer 18

Ok, so I tried Normalcdf(-1.38,-2.24,0,1) and it didn't work

Answer 19

now swap the high and low about

Normalcdf(-2.24,-1.38,0,1)

that should work out

Answer 20

Ugh nope. Not that either... What am I doing wrong? Should it be Normalpdf?

Answer 21

pdf isnt valid here.

and i cant be sure that youve hit the buttons correctly :)

Answer 22

assuming you eventually get the hang of it, it shold give you a solution similar to this

http://www.wolframalpha.com/input/?i=P%28-2.24%3Cz%3C-1.38%29

Answer 23

CDF means: cumulative distribution function

we are finding the sum of the area between 2 points, is a cumulative sum so we use the CDF function

Answer 24

So it would then be 0.07 for the probability? How can I get into Wolfram? (For free)

Answer 25

PDF is a probability distribution function, and it relates to a single point ... ive never had a need to use the PDF function

Answer 26

Or 0.071 I can't figure out the rounding..

Answer 27

i use the wolf for free all the time ...

Answer 28

what do you have to round to? what number of deies?

Answer 29

** decies

Answer 30

Hmmm for some reason it never lets me. Maybe I just don't know how to find what I am trying to input and look for I guess

Answer 31

Four decimal places as needed

Answer 32

the syntax can be daunting i agree. its taken me a few years to learn the little I have for it

Answer 33

Ok figured it out on my ti83 and I got -.071247

Answer 34

then 2 or 3 decies is not appropriate ..

07120 < 07124 < 07130
4 6


we are closer to 0712

Answer 35

I make that into a positive right?

Answer 36

the negative is bad lol ... ignore that sign

Answer 37

most likely your high,low values are mixed around.

Answer 38

Ok lol! Thank you!!!

Answer 39

yep

Answer 40

I have plenty more that I still have that I am still confused about so you'll probably see me on here quite a bit

Answer 41

as long as you can recall what it is we need to use, and if im about, ill try to guide your efforts

Answer 42

Thank you so much