The quantile or probit function, as you can see from the link (see "Computatuon"), is computed with inverse gaussian error function 
which I hope is downloadable for calculators like TI-89. Look here for instance.
Top answer 1 of 3
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The quantile or probit function, as you can see from the link (see "Computatuon"), is computed with inverse gaussian error function which I hope is downloadable for calculators like TI-89. Look here for instance.
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2nd Vars (Distr)>"InvNorm" next you subtract 1-% and enter this into your Inverse Norm along with your Mean and standard deviation.
Ex: Find the third quartile Q3 which is the IQ score separating the top 25% from the others. With a Mean of 100 and a Standard Deviation of 15.
1-.25=.75 in Inv Norm (.75,100,15)=110 My answer is 110
University of North Dakota
cs.uni.edu › › ~campbell › stat › normfact.html
Important z-scores
It is readily calculated that for the standard normal distribution the first quartile is -.67 (using .2514 for .25) and the third quartile is .67.
Videos
06:23
2 - Quartiles of Normal Distributions - YouTube
Normal Distribution 7 For a normal distribution mean is 50 and ...
08:46
Finding Interquartile Range Using Normal Distribution - YouTube
03:35
Finding Interquartile Range IQR in Normally Distributed Data - YouTube
How do I calculate the first quartile?
To determine the first quartile:
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Sort your data in ascending order.
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Determine the lower half of your data:
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Even number of points: split your set exactly in half and take the lower (left) half.
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Odd number of points: take all numbers to the left of the number exactly in the middle.
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Find the median of the lower half:
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Even number of data points: take the average of the two values in the middle.
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Odd number of data points: take the number right in the middle.
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You've found the lower quartile!
omnicalculator.com
omnicalculator.com › statistics › first-quartile
First Quartile Calculator
What is the first quartile?
The first quartile (a.k.a. the lower quartile) is a measurement of position in a data set. It is the value that marks one quarter (25%) of data points sorted in ascending order. That is, 25% of the data points are less than the first quartile, and 75% of data points are greater than the first quartile. In other words, the lower quartile is the 25th percentile. The lower quarter is most often denoted as Q1.
omnicalculator.com
omnicalculator.com › statistics › first-quartile
First Quartile Calculator
Where is the first quartile in a box plot?
The lower quartile is the bottom side of a vertical box plot and the left side of a horizontal box plot. The other (top/right) side corresponds to the upper (third) quartile. The line inside the box is the median (the second quartile).
omnicalculator.com
omnicalculator.com › statistics › first-quartile
First Quartile Calculator
GIGACalculator.com
gigacalculator.com › calculators › statistics › normal distribution calculator
Normal Distribution Calculator with Formulas & Definitions
Calculate p-value from Z score or Z score from P-value. ➤ Standard normal distribution calculator (z table calculator) which also supports custom mean and sd (standard deviation, sigma). Inverse normal distribution calculator (invnorm). Normal distribution formulas: probability density, cumulative distribution function and quantile function.
Statology
statology.org › home › how to find quartiles using mean & standard deviation
How to Find Quartiles Using Mean & Standard Deviation
September 27, 2021 - You can use the following formulas to find the first (Q1) and third (Q3) quartiles of a normally distributed dataset: Q1 = μ - (.675)σ Q3 = μ + (.675)σ
Quora
quora.com › How-do-you-find-the-first-quartile-of-a-normal-distribution
How to find the first quartile of a normal distribution - Quora
Answer (1 of 2): You will need either a calculator which can calculate a normal distribution or a table of the normal distribution. I am using the table at Standard Normal Distribution Table Then you have to do a backward lookup of 0.25. In other words, find numbers as close as you can to 0.25 i...
Omni Calculator
omnicalculator.com › statistics › first-quartile
First Quartile Calculator
October 3, 2025 - IQR is a measure of spread about the median: the smaller the IQR, the more your data is clumped. In any normal distribution, Q1 = μ - 0.67448σ, where μ stands for the mean and σ for the standard deviation of the distribution in question.
MathBitsNotebook
mathbitsnotebook.com › Algebra2 › Statistics › STstandardNormalDistribution.html
Standard Normal Distribution - MathBitsNotebook(A2)
Algebra 2 Lessons and Practice is a free site for students (and teachers) studying a second year of high school algebra.
YouTube
youtube.com › watch
Find the first Quartile Q_1 with the Normal Distribution and StatCrunch - YouTube
Please Subscribe here, thank you!!! https://goo.gl/JQ8NysFind the first Quartile Q_1 with the Normal Distribution and StatCrunch
Published September 4, 2018
HackMath
hackmath.net › en › calculator › quartile-q1-q3
Quartile calculator Q1, Q3 (statistics)
The online calculator computes the first (lower), second (median), and third (upper) quartiles from a set of numerical data. These quartiles are equal to the 25th, 50th, and 75th percentile.
PlanetCalc
planetcalc.com › 4987
Online calculator: Normal Distribution Quantile function
Calculates Normal distribution quantile value for given mean and variance. Set variance = 1 and mean to zero to calculate Probit function value.
CalculatorSoup
calculatorsoup.com › calculators › statistics › quartile-calculator.php
Quartile Calculator | Interquartile Range Calculator
This quartile calculator and interquartile range calculator finds first quartile Q1, second quartile Q2 and third quartile Q3 of a data set.
YouTube
youtube.com › watch
Find the Quartiles of any Normal Distribution in 2 Minutes - YouTube
Introducing the four quartiles of the normal distribution and how to find them fast.👉Click here for all videos related to normal distribution: https://www.y...
Published March 24, 2023
Investopedia
investopedia.com › terms › q › quartile.asp
Understanding Quartiles: Definitions, Calculations, and Examples
August 3, 2025 - This division helps identify the spread and distribution of data values. The median, a measure of central tendency, divides a data set into two halves. Quartiles further break down the data set into quarters, which include a lower quartile (25% mark), median (50% mark), and upper quartile (75% mark). Calculating quartiles can be done manually using formulas or more efficiently in spreadsheets using functions like QUARTILE, allowing for quick analysis of data sets.
Scribbr
scribbr.com › home › quartiles & quantiles | calculation, definition & interpretation
Quartiles & Quantiles | Calculation, Definition & Interpretation
June 21, 2023 - Count the number of observations ... ... Calculate n * (1 / 4). If n * (1 / 4) is an integer, then the first quartile is the mean of the numbers at positions n * (1 / 4) and n * (1 / 4) + 1....
MathCracker
mathcracker.com › quartile-calculator
Quartile Calculator - MathCracker.com
February 3, 2020 - Instructions: This quartile calculator ... you specify in the form below: The k-th quartile (first, second or third quartile) of a distribution corresponds to a point with the property that 25% of the ......
Allthingsstatistics
allthingsstatistics.com › home › quartiles for normal distribution
Quartiles for Normal Distribution - All Things Statistics
April 8, 2023 - First Quartile = μ – 0.675σ. Second Quartile = μ. Third Quartile = μ + 0.675σ. Let X be a random variable that follows the normal distribution with mean μ and variance σ2.
Boston University
sphweb.bumc.bu.edu › otlt › mph-modules › bs › bs704_probability › bs704_probability10.html
Computing Percentiles
... The mean BMI for men aged 60 ... below it and 10% above it, as illustrated in the figure below. To compute the 90th percentile, we use the formula X=μ + Zσ, and we will use the standard normal distribution table, except that we will work in the opposite directio...
Critical Value Calculator
criticalvaluecalculator.com › quartile-calculator
Quartile Calculator
October 6, 2025 - Welcome to the quartile calculator, where we'll learn how to calculate quartiles of a dataset. In fact, whenever we have a collection of numbers that we want to understand better using statistics, finding the quartiles is one of the first things that comes to mind.
Statistics Canada
www150.statcan.gc.ca › n1 › edu › power-pouvoir › ch12 › 5214890-eng.htm
4.5.1 Calculating the range and interquartile range
The range only takes into account ... of the distribution. It's used as a supplement to other measures, but it is rarely used as the sole measure of dispersion because it’s sensitive to extreme values. The interquartile range and semi-interquartile range give a better idea of the dispersion of data. To calculate these two measures, you need to know the values of the lower and upper quartiles. The lower quartile, or first quartile (Q1), ...
Statistics How To
statisticshowto.com › home › probability and statistics topics index › interquartile range (iqr): what it is and how to find it
Interquartile Range (IQR): What it is and How to Find it - Statistics How To
October 10, 2024 - To tell whether a population is normally distributed, solve both equations and then compare the results. If there is a significant difference between the results and the first or third quartiles, then the population is not normally distributed.