Z Score

survival · 2011-05-05 07:59:51

The box of cereal again:
A box of cereal contains 458 g with a standard deviation of 10.02. Find that the jar contains more than 468 g. Assume normal distribution. Use a z - score rounded to the hundreds.
The probability that the cereal contains more than 468 g. is_______________

T/Y

Last edited by survival (2011-05-05 13:43:11)

survival · 2011-05-05 13:22:47

bobbym, where are you?

bobbym · 2011-05-05 14:39:16

Hi survival;

Having some things to deal with at home has tied me up today.

I am getting .16, the actual answer is .1591, I have rounded it the hundredths.

survival · 2011-05-05 15:07:54

T/Y and good evening.

bobbym · 2011-05-05 15:16:38

Good evening. How are you? Any more math left?

survival · 2011-05-05 19:50:04

Thanks, i figured it out.

survival · 2011-05-05 19:52:13

bobbym wrote:

Good evening. How are you? Any more math left?

I am just tired that is all. No more math for now, but I will still visit the board. This is board where you can learn, and I like that.
ps. the answer about the cereal was off just a little, but that is okay.

Last edited by survival (2011-05-05 19:53:26)

bobbym · 2011-05-05 19:59:29

How far off?

survival · 2011-05-06 11:05:05

I read it incorrectly. It wanted rounding to the thousandth and I think I put it in as a tenth.
What exactly do you subtract when the z score is not on the chart, as in--in between? How do you know what to subtract from the equation to get the correct answer?

bobbym · 2011-05-06 12:27:05

Hi survival;

You could do a linear interpolation between two values. Or you could find out how your teacher rounds these types of numbers.

Can I see an example and I will show you what I do. Your teachers answers may not be close enough to mine for there to be a match. So, I have been trying to guess what he/she wants. This is the most pragmatic approach.

survival · 2011-05-07 20:34:36

hello,
well, it's done from that chart that has area and z scores. It gives the area. Then usually when the equation is near being solved, you subtract an unknown number from the one you have from the area to arrive at the z score. It's all from the chart, but never close to the area you find. If that makes any sense. It's not what he or she wants, it's the solution to the equation.

bobbym · 2011-05-07 21:04:01

Hi;

It will be clearer if I see what problem you are talking about.

survival · 2011-05-08 01:59:59

Hello,
I will find something later. Up all night watching movies on the lap top. Now, I sleep.
PS Oh, I remember. It was the first problem I posted about the cereal. The very first, I think.

bobbym · 2011-05-08 04:22:15

Okay, see you then. I have been watching movies too.

survival · 2011-05-13 09:24:20

bobbym wrote:

Hi survival;
Having some things to deal with at home has tied me up today.
I am getting .16, the actual answer is .1591, I have rounded it the hundredths.

Hello, I pulled up this problem and the actual answer was. 0.164.

Ya know something? I also noticed that the ones, I missed parts of, were mistakes that I made from not reading the problem correctly or just silly stupid mistakes that was negligence on my part. I knew them all in the one that had the cereal box, yet came out with 85.6.
I saw that cereal problem a lot of times and missed the thing every time I encountered it. Nonsense! Actually, once I even asked the instructor to explain it to me. The mind can only hold so much until it rests and then begins again.

bobbym · 2011-05-13 09:47:45

Hi survival;

I see now why your instructors answers are kaboobly doo. The z tables are rounded and if you round the z scores before you even look at the table the answers lose all accuracy.

If he/she knew anything at all. If he/she had ever worked in a real place, he/she would know that we do not even use z tables. There is excellent software to do it.

If you require I will rework the problem and try to do as Mr. Kaboobly doo would.

survival · 2011-05-13 11:42:22

bobbym wrote:

Hi survival;

If you require I will rework the problem and try to do as Mr. Kaboobly doo would.

Well, actually it was the online system that made the decision of answers. If you can work it to what the website wanted, then I would like to see how it arrived there. Thanks.

bobbym · 2011-05-13 13:26:38

That is the z score rounded to the nearest hundred.

Use this z chart:

http://www.regentsprep.org/Regents/math … ZChart.htm

Read off z.98 = .8365

P = 1 - .8367 = .1635 ≈ .164

survival · 2011-05-13 16:57:38

Thank you!
I am not that good with reading tables. I see the answer, and everything else on the table, but how do you know the 1 is to be subtracted? This is what I meant when I said that I didn't understand the "between." When they are not between then it is easier to arrive at the answer. Does this serve a purpose and if so what is it?

bobbym · 2011-05-13 17:17:48

Hi;

Refer to the drawing below.

The area marked in red is .8365 It represents the probability of less than 468 gms or .98 standard deviations. The area to the right of the line marked .98 sd is everything greater than 468 gms. That is what you want.

See that bell shaped curve, that is the normal distribution. The entire area under it is equal to 1. So:

Area in red + Area you want = 1

.8365 + Area you want = 1

Subtract .8365 from both sides.

(.8365 - .8365 ) + Area you want = 1 - .8365

(0) + Area you want = 1 - .8365

Area you want = 1 - .8365

survival · 2011-05-13 17:47:08

Now, we're getting somewhere. I can see it, which makes a difference.
You drew that exactly like one of my professors. He would draw the curve, mark the lines off, then go 3 dots on each side and go from there. Math instructors talk too fast, so sometimes you miss stuff. I do want to understand, and I have come far.

I asked before if you were a teacher or professor, and you replied that you taught your brother. It's just my observation/opinion, but you demonstrated that just like a professor would. Are you still teaching? I believe you said you were fond of statistics?
Thank you for explaining this so well. I never stop asking questions, sometimes it gets on people's nerves. That is why I did so well in journalism and interviewing people.

Last edited by survival (2011-05-13 17:55:43)

bobbym · 2011-05-13 18:04:49

I post on this forum and a couple others. That is it. Yes, I taught my brother. He is a brilliant guy and learned it all very quickly. I was also instructing a girl but she went over to the dark side of the force.

I believe you said you were fond of statistics?

I like Combinatorics, Probability ( statistics ), Numerical Analysis and Number theory best.

Are you still teaching?

I never taught in classrooms. That is a little bit out of my league. I learned math and computers the hard way. Do not learn, do not eat, simple as that. Since I am very dense, I guess it was God's way of forcing some knowledge into a monkey brain.

survival · 2011-05-13 20:50:56

I believe you said you were fond of statistics?

I like Combinatorics, Probability ( statistics ), Numerical Analysis and Number theory best.

You mean such as toss of the dice and how many tosses will it take to get a 9, etc.? That is one of the classes I finished. It was interesting. I did not understand Truth Tables though. You know T T F F and so on. I never caught onto that. After the first three rows, it was a bit confusing.

Are you still teaching?

I never taught in classrooms. That is a little bit out of my league. I learned math and computers the hard way. Do not learn, do not eat, simple as that. Since I am very dense, I guess it was God's way of forcing some knowledge into a monkey brain.

Well, you are teaching here too, helping those of us who have not a clue on some math. I never knew math forums existed until I was having such a rough time and googled it. That is how I landed here. I wish I had done that last semester when I had Algebra. It was terribly confusing. A lot more complicated than what I just completed.
Oh, it is late/early and I am still typing. I posted a blog on myspace. Have not been there in a very long time.

bobbym · 2011-05-13 21:03:03

Yes, problems like that and much tougher ones.

Algebra is not at all tough.

survival · 2011-05-14 15:33:25

bobbym wrote:

Yes, problems like that and much tougher ones.
Algebra is not at all tough.

Not tough? It nearly drove me nuts!

Math Is Fun Forum

#1 2011-05-05 07:59:51

Z Score

#2 2011-05-05 13:22:47

Re: Z Score

#3 2011-05-05 14:39:16

Re: Z Score

#4 2011-05-05 15:07:54

Re: Z Score

#5 2011-05-05 15:16:38

Re: Z Score

#6 2011-05-05 19:50:04

Re: Z Score

#7 2011-05-05 19:52:13

Re: Z Score

#8 2011-05-05 19:59:29

Re: Z Score

#9 2011-05-06 11:05:05

Re: Z Score

#10 2011-05-06 12:27:05

Re: Z Score

#11 2011-05-07 20:34:36

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#12 2011-05-07 21:04:01

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#13 2011-05-08 01:59:59

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#14 2011-05-08 04:22:15

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#15 2011-05-13 09:24:20

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#16 2011-05-13 09:47:45

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#17 2011-05-13 11:42:22

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#18 2011-05-13 13:26:38

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#19 2011-05-13 16:57:38

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#20 2011-05-13 17:17:48

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#21 2011-05-13 17:47:08

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#22 2011-05-13 18:04:49

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#23 2011-05-13 20:50:56

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#24 2011-05-13 21:03:03

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#25 2011-05-14 15:33:25

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