What is the Gauss curve have to do with this?

For the empirical rule to be valid the data must be normally distributed, so the rules for percentages in the problems above would not hold true if the data didn't follow a gaussian or normal distribution.

I answered the last question in the following way. I figured out the z score which was 0.9772 for value that is two standard deviations above normal. Therefore one can deduce that the sample size that lies to the right of this should be 0.0228 (1-0.9772). That multiplied by 400 gives me 9.1 approximated to 9. What is wrong with this method?

I agree that using the z-Score is the most accurate answer. The answer given is using approximations of the normal and are not as accurate.

what if they ask you to solve for standard deviation with only knowing the range

This question is not really meaningful for a normal distribution, since all normal distributions have infinite range. For general data sets, knowing the range of a data set is not sufficient for finding its standard deviation. For example, the data sets 1,5,5,9 and 1,2,8,9 both have range 9-1=8, but 1,2,8,9 has the larger standard deviation because the values are spread out farther from the mean (5). Have a blessed, wonderful day!

Is there a table or cheat sheet I can use to help with the subject?

Here is a website that has z-tables for positive and negative z-scores as well as other things related to this subject: https://z-scoretable.com/. There are plenty of z-tables on Google Images as well. Hope this helps!😄

where does the 13.5% come from in question 3?

Empirical rule! Ok, so 95% of the observations are within 2 standard deviations of the mean, and 68% of the observations are within 1 standard deviation of the mean, right? Let's find the difference between 2 s.d. and 1 s.d. It will be 95%-68%=27%. But you have to divide this 27% by 2 because you have to find the percentage between 105 and 115 millimeters. There comes 13.5%!

Main content

Statistics and probability

Course: Statistics and probability > Unit 4

Lesson 6: Normal distribution calculations

Basic normal calculations

AP.STATS:

VAR‑2 (EU)

VAR‑2.A (LO)

VAR‑2.A.3 (EK)

CCSS.Math:

HSS.ID.A.4

Google Classroom

Many measurements fit a special distribution called the normal distribution. In a normal distribution,

approximately equals, 68, percent of the data falls within 1 standard deviation of the mean
approximately equals, 95, percent of the data falls within 2 standard deviations of the mean
approximately equals, 99, point, 7, percent of the data falls within 3 standard deviations of the mean

Problem 1

A large sample of females had their systolic blood pressure measured. The mean blood pressure was 125 millimeters of mercury and the standard deviation was 10 millimeters of mercury.

Which normal distribution below best summarizes the data?

Problem 2

What percent of females had blood pressures between 105 and 135 millimeters of mercury?

percent

Problem 3

The sample had a total of 400 females that participated.

About how many females in the sample had blood pressures higher than 145 millimeters of mercury?

approximately equals

females

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Tushar
Posted 7 years ago. Direct link to Tushar's post “What is the Gauss curve h...”
What is the Gauss curve have to do with this?
Button navigates to signup pageComment on Tushar's post “What is the Gauss curve h...”
(10 votes)
Answer
- jasongulley
  Posted 7 years ago. Direct link to jasongulley's post “For the empirical rule to...”
  For the empirical rule to be valid the data must be normally distributed, so the rules for percentages in the problems above would not hold true if the data didn't follow a gaussian or normal distribution.
  Comment on jasongulley's post “For the empirical rule to...”
  (23 votes)
venkataramanareddy.t.a
Posted 6 years ago. Direct link to venkataramanareddy.t.a's post “I answered the last quest...”
I answered the last question in the following way. I figured out the z score which was 0.9772 for value that is two standard deviations above normal. Therefore one can deduce that the sample size that lies to the right of this should be 0.0228 (1-0.9772). That multiplied by 400 gives me 9.1 approximated to 9. What is wrong with this method?
Button navigates to signup pageComment on venkataramanareddy.t.a's post “I answered the last quest...”
(9 votes)
Answer
- tomthorpe55
  Posted 6 years ago. Direct link to tomthorpe55's post “I agree that using the z-...”
  I agree that using the z-Score is the most accurate answer. The answer given is using approximations of the normal and are not as accurate.
  Comment on tomthorpe55's post “I agree that using the z-...”
  (8 votes)
721281
Posted 7 years ago. Direct link to 721281's post “where does the 13.5% come...”
where does the 13.5% come from in question 3?
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(0 votes)
Answer
- RacheLee
  Posted 7 years ago. Direct link to RacheLee's post “Empirical rule! Ok, so 95...”
  Empirical rule!
  Ok, so 95% of the observations are within 2 standard deviations of the mean, and 68% of the observations are within 1 standard deviation of the mean, right?
  Let's find the difference between 2 s.d. and 1 s.d. It will be 95%-68%=27%. But you have to divide this 27% by 2 because you have to find the percentage between 105 and 115 millimeters. There comes 13.5%!
  Comment on RacheLee's post “Empirical rule! Ok, so 95...”
  (12 votes)
TheYoungMind2019 Carol_Irizarry
Posted 7 years ago. Direct link to TheYoungMind2019 Carol_Irizarry's post “Are these realistic stati...”
Are these realistic statistics? They better not be, my math teacher commonly uses extremely unrealistic stats, it's funny.
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(3 votes)
Answer
axel7155
Posted 6 years ago. Direct link to axel7155's post “what if they ask you to s...”
what if they ask you to solve for standard deviation with only knowing the range
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(2 votes)
Answer
- Ian Pulizzotto
  Posted 6 years ago. Direct link to Ian Pulizzotto's post “This question is not real...”
  This question is not really meaningful for a normal distribution, since all normal distributions have infinite range.
  
  For general data sets, knowing the range of a data set is not sufficient for finding its standard deviation. For example, the data sets 1,5,5,9 and 1,2,8,9 both have range 9-1=8, but 1,2,8,9 has the larger standard deviation because the values are spread out farther from the mean (5).
  
  Have a blessed, wonderful day!
  Button navigates to signup page
  (2 votes)
elarson
Posted 22 days ago. Direct link to elarson's post “Why, just why?”
Why, just why?
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(2 votes)
Answer
Iron Programming
Posted 3 years ago. Direct link to Iron Programming's post “For the titles of Article...”
For the titles of Articles, Videos, and Skills; should the wording follow the same grammar rules as the title of a book does?
e.g.: Should the titles be capitalized with the exception of conjunctions like and/or/but/ect?

I'm slightly confused, because KA only capitalizes the first word, but I can't find anywhere on the web where it tells you how to properly right the title.

Any help?

I'm slightly confused...
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(2 votes)
Answer
- Error 404
  Posted 6 months ago. Direct link to Error 404's post “Khan Academy is an except...”
  Khan Academy is an exception to the usually title rules. Sometimes websites might only capitalize the first word or not follow the exact rules as in a book for some videos and articles. You are correct though, that rule is used commonly in books, movies, etc.
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  (1 vote)
Jy'mirr
Posted 24 days ago. Direct link to Jy'mirr's post “whats the answers twin?”
whats the answers twin?
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(2 votes)
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Karl DeQuillettes
Posted 2 years ago. Direct link to Karl DeQuillettes's post “Is there a table or cheat...”
Is there a table or cheat sheet I can use to help with the subject?
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(1 vote)
Answer
- green_ninja
  Posted 2 years ago. Direct link to green_ninja's post “Here is a website that ha...”
  Here is a website that has z-tables for positive and negative z-scores as well as other things related to this subject: https://z-scoretable.com/.
  
  There are plenty of z-tables on Google Images as well.
  
  Hope this helps!😄
  Comment on green_ninja's post “Here is a website that ha...”
  (3 votes)
John Orozco
Posted 6 years ago. Direct link to John Orozco's post “So all of the boundaries ...”
So all of the boundaries are supposed to add up to 100%?
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(1 vote)
Answer
- Nabil Daoud
  Posted 6 years ago. Direct link to Nabil Daoud's post “The data that falls withi...”
  The data that falls within 1 standard deviation of the mean is a subset (part) of the data that falls within 2 standard deviations. As you go out to three and four standard deviations you quickly (but asymptotically) approach 100%.
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  (1 vote)