# 2.11 Summary of formulas

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A summary of useful formulas used in examining descriptive statistics

## Commonly used symbols

• The symbol $\Sigma$ means to add or to find the sum.
• $n$ = the number of data values in a sample
• $N$ = the number of people, things, etc. in the population
• $\overline{x}$ = the sample mean
• $s$ = the sample standard deviation
• $\mu$ = the population mean
• $\sigma$ = the population standard deviation
• $f$ = frequency
• $x$ = numerical value

## Commonly used expressions

• $x*f$ = A value multiplied by its respective frequency
• $\sum x$ = The sum of the values
• $\sum x*f$ = The sum of values multiplied by their respective frequencies
• $\left(x-\overline{x}\right)$ or $\left(x-\mu \right)$ = Deviations from the mean (how far a value is from the mean)
• ${\left(x-\overline{x}\right)}^{2}$ or ${\left(x-\mu \right)}^{2}$ = Deviations squared
• ${f\left(x-\overline{x}\right)}^{2}$ or ${f\left(x-\mu \right)}^{2}$ = The deviations squared and multiplied by their frequencies

Mean Formulas:

• $\overline{x}=$ $\frac{\sum x}{n}$ or $\overline{x}=$ $\frac{\sum f·x}{n}$
• $\mu =$ $\frac{\sum x}{N}$ or $\mu$ = $\frac{\sum f·x}{N}$

Standard Deviation Formulas:

• $s=$ $\sqrt{\frac{\Sigma {\left(x-\overline{x}\right)}^{2}}{n-1}}$ or $s=$ $\sqrt{\frac{\Sigma {f·\left(x-\overline{x}\right)}^{2}}{n-1}}$
• $\sigma =$ $\sqrt{\frac{\Sigma {\left(x-\overline{\mu }\right)}^{2}}{N}}$ or $\sigma =$ $\sqrt{\frac{\Sigma {f·\left(x-\overline{\mu }\right)}^{2}}{N}}$

Formulas Relating a Value, the Mean, and the Standard Deviation:

• value = mean + (#ofSTDEVs)(standard deviation), where #ofSTDEVs = the number of standard deviations
• $x$ = $\overline{x}$ + (#ofSTDEVs)( $s$ )
• $x$ = $\mu$ + (#ofSTDEVs)( $\sigma$ )

explain and give four Example hyperbolic function
The denominator of a certain fraction is 9 more than the numerator. If 6 is added to both terms of the fraction, the value of the fraction becomes 2/3. Find the original fraction. 2. The sum of the least and greatest of 3 consecutive integers is 60. What are the valu
1. x + 6 2 -------------- = _ x + 9 + 6 3 x + 6 3 ----------- x -- (cross multiply) x + 15 2 3(x + 6) = 2(x + 15) 3x + 18 = 2x + 30 (-2x from both) x + 18 = 30 (-18 from both) x = 12 Test: 12 + 6 18 2 -------------- = --- = --- 12 + 9 + 6 27 3
Pawel
2. (x) + (x + 2) = 60 2x + 2 = 60 2x = 58 x = 29 29, 30, & 31
Pawel
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Ifeanyi
on number 2 question How did you got 2x +2
Ifeanyi
combine like terms. x + x + 2 is same as 2x + 2
Pawel
Mark and Don are planning to sell each of their marble collections at a garage sale. If Don has 1 more than 3 times the number of marbles Mark has, how many does each boy have to sell if the total number of marbles is 113?
Mark = x,. Don = 3x + 1 x + 3x + 1 = 113 4x = 112, x = 28 Mark = 28, Don = 85, 28 + 85 = 113
Pawel
how do I set up the problem?
what is a solution set?
Harshika
find the subring of gaussian integers?
Rofiqul
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Abdullahi
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Mark
find the value of 2x=32
divide by 2 on each side of the equal sign to solve for x
corri
X=16
Michael
Want to review on complex number 1.What are complex number 2.How to solve complex number problems.
Beyan
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Mark
use the y -intercept and slope to sketch the graph of the equation y=6x
how do we prove the quadratic formular
Darius
hello, if you have a question about Algebra 2. I may be able to help. I am an Algebra 2 Teacher
thank you help me with how to prove the quadratic equation
Seidu
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Opoku
what is math number
4
Trista
x-2y+3z=-3 2x-y+z=7 -x+3y-z=6
can you teacch how to solve that🙏
Mark
Solve for the first variable in one of the equations, then substitute the result into the other equation. Point For: (6111,4111,−411)(6111,4111,-411) Equation Form: x=6111,y=4111,z=−411x=6111,y=4111,z=-411
Brenna
(61/11,41/11,−4/11)
Brenna
x=61/11 y=41/11 z=−4/11 x=61/11 y=41/11 z=-4/11
Brenna
Need help solving this problem (2/7)^-2
x+2y-z=7
Sidiki
what is the coefficient of -4×
-1
Shedrak
the operation * is x * y =x + y/ 1+(x × y) show if the operation is commutative if x × y is not equal to -1
A soccer field is a rectangle 130 meters wide and 110 meters long. The coach asks players to run from one corner to the other corner diagonally across. What is that distance, to the nearest tenths place.
Jeannette has $5 and$10 bills in her wallet. The number of fives is three more than six times the number of tens. Let t represent the number of tens. Write an expression for the number of fives.
What is the expressiin for seven less than four times the number of nickels
How do i figure this problem out.
how do you translate this in Algebraic Expressions
why surface tension is zero at critical temperature
Shanjida
I think if critical temperature denote high temperature then a liquid stats boils that time the water stats to evaporate so some moles of h2o to up and due to high temp the bonding break they have low density so it can be a reason
s.
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
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