Answer:
Step-by-step explanation:
a) So... To work out the average or mean age we must first calculate the total age.
19 x 2 = 38
20 x 3 = 60
21 x 1 = 21
22 x 4 = 88
23 x 1 = 23
Total = 230
Then... Divide the number of players with this figure
Number of players = 2 + 3 + 2 + 4 + 1 = 11
230/11 = 20.9 is the average age of the players
b) We know the average will now be 22 and we know the number of players is now 12.
So... 22 x 12 = 264 (This will be the new total age of all the players)
We know the previous total was 230
So.. 264-230 = 34 (years old)
Hope this helps
X^4-13x^2+36 =
a. (x - 2)2(x - 3)2
b. (x2 + 4)(x 2 + 9)
C. (x - 2)(x + 2)(x - 3)(x + 3)
d. (x2 - 4)(x 2 + 9)
Answer:
answer C
Step-by-step explanation:
hello,
[tex]x^4-13x^2+36=(x^2-4)(x^2-9)[/tex]
as the sum of the zeroes are 13 and their product 36
4 + 9 = 13
4 * 9 = 36
and then we can write
[tex](x^2-4)=(x-2)(x+2)\\(x^2-9)=(x-3)(x+3)[/tex]
so
[tex]x^4-13x^2+36=(x^2-4)(x^2-9) = (x-2)(x+2)(x-3)(x+3)[/tex]
hope this helps
(09.06 HC)
The function H(t) = -16t2 + 90t + 75 shows the height H(t), in feet, of a projectile after t seconds. A
second object moves in the air along a path represented by g(t) = 31 + 32.2t, where g(t) is the height, in
feet, of the object from the ground at time t seconds.
Part A: Create a table using integers 2 through 5 for the 2 functions. Between what 2 seconds is the
solution to H(t) = g(t) located? How do you know? (6 points)
Part B: Explain what the solution from Part A means in the context of the problem.(4 points)
Answer: h(t) = g(t) between 4 and 5 seconds
Step-by-step explanation:
h(t) = -16t² + 90t + 75
g(t) = 31 + 32.2t
[tex]\begin{array}{c|c|c|c|c}\qquad&\underline{\quad t=2\quad }&\underline{\quad t=3\quad}&\underline{\quad t=4\quad }&\underline{\quad t=5\quad }\\h(t)&191&201&179&125\\g(t)&95.4&127.6&159.8&192\end{array}\right][/tex]
Notice that g(t) is increasing from t=2 to t=5, while h(t) is increasing from t=2 to t=3 and then decreasing.
At t=4, h(t) > g(t)
At t = 5, g(t) > h(t)
therefore, the two lines must intersect at a point between t=4 and t=5.
You can graph this to verify the answer.
Construct a confidence interval of the population proportion at the given level of confidence.
x equals =860
n equals =1200
94% confidence
The lower bound of the confidence interval is __?
Answer:
The lower bound of the confidence interval is 0.6922.
Step-by-step explanation:
We have to calculate a 94% confidence interval for the proportion.
The sample proportion is p=0.7167.
[tex]p=X/n=860/1200=0.7167[/tex]
The standard error of the proportion is:
[tex]\sigma_p=\sqrt{\dfrac{p(1-p)}{n}}=\sqrt{\dfrac{0.7167*0.2833}{1200}}\\\\\\ \sigma_p=\sqrt{0.000169}=0.013[/tex]
The critical z-value for a 94% confidence interval is z=1.8808.
The margin of error (MOE) can be calculated as:
[tex]MOE=z\cdot \sigma_p=1.8808 \cdot 0.013=0.0245[/tex]
Then, the lower and upper bounds of the confidence interval are:
[tex]LL=p-z \cdot \sigma_p = 0.7167-0.0245=0.6922\\\\UL=p+z \cdot \sigma_p = 0.7167+0.0245=0.7412[/tex]
The 94% confidence interval for the population proportion is (0.6922, 0.7412).
Select the expression that is equivalent to (x - 1)2.
O A. x2 - 2x + 2
O B. x2 - x + 2
O C. x2 - x + 1
O D. x2 – 2x + 1
Answer:
D
Step-by-step explanation:
(x - 1)² = (x - 1)(x - 1)
x² - x- x + 1 = x² - 2x + 1
Easy geometry just find area shade boxes thank you plz help
Answer:
45 square units
Step-by-step explanation:
To figure out the area of a trapezoid, the formula is. A= (b1 + b2)h ÷2 . b1 is the top side which is 7 units and b2 is the bottom side which is 11 units. The height (h) is a vertical line going from the top to the bottom which is 5 units. All you need to do now is plug in those numbers and solve the equation.
Answer: 45 square units
Step-by-step explanation:
This shape can be broken down into two diffrent peices
The first peice is the rectangle
The second peice is the triangle
And both of these peices area's added together will yeild the total area
The rectangle is 7 units long and 5 units high, so it has an area of (7X5) = 35
The triangle is a little bit more complicated, it's formula is (BaseXHeight)/4
So all we need to do is plug in The base of the triangle = 4
And the Height of the trianlge = 5
So the triangles area is... (4X5)/2= 10
35+10=45 square units
Which equation, when solved, gives 8 for the value of x?
A: 5/2x+7/2x=3/4x+14
B: 5/4x-9=3/2x-12
C: 5/4x-2=3/2x-4
D: 5/2x-7=3/4x+14
Answer:
Step-by-step explanation:
C. 5x/4-2=3x/2-4
5x/4 -2=6x/4-4
+4 +4
5x/4+2=6x/4
-5x/4
2=x/4
*4
x=8
Answer:
your answer is C
Step-by-step explanation:
Box A contains 5green and 7 red balls. Box B contains 3green, 3 red and 6 yellow balls. A box is sleeted at random and a ball is drawn at random from it. What is the probability that the drawn ball is green?
Answer:
5/48Step-by-step explanation:
Given
the sample space for box A
green balls = 5
red balls= 7
sample size= 5+7= 12
the sample space for box B
green balls = 3
red balls= 3
yellow balls= 6
sample size= 3+3+6= 12
The probability of drawing a green ball from box A= 5/12
The probability of drawing a green ball from box B= 3/12= 1/4
Therefore the probability of picking a green ball from either of the boxes at random is =[tex]=\frac{5}{12} *\frac{1}{4}[/tex][tex]=\frac{5}{48}[/tex]
Arrange in ascending order. 8/13, 2/9,28/29
Step-by-step explanation:
he operation of sorting fractions in ascending order: 18/46, 28/41, 29/38, 29/44, 32/30 ... terms equivalents: 18/46=(2×3^2)/(2×23)=((2×3^2)÷2)/((2×23)÷2)=9/23; 28/41 already reduced to ... by the largest exponents: LCM (9, 28, 29)=2^2×3^2× 7×29=7308 Calculate LCM, the least ... /10 </13 </19
solve for n n/5+0.6=2
Answer:
N=7
Step-by-step explanation:
It is correct on Khan
Find the values of x and y in these equations. (x + yi) + (4 + 6i) = 7 − 2i (equation A) (x + yi) − (-8 + 11i) = 5 + 9i (equation B)
Answer:
Step-by-step explanation:
(x+yi)+4+6i=7-2i
x+yi=7-2i-4-6i
x+yi=3-8i
equating real and imaginary parts
x=3,y=-8
B.
x+yi=5+9i+(-8+11i)
x+yi=5+9i-8-11i
x+yi=-3-2i
equating real ,and imaginary parts
x=-3
y=-2
The value of x and y for equation A is
[tex]x=3, y=-8[/tex]
The value of x and y for equation B is
[tex]x=-3 , y=20[/tex]
Given :
[tex](x + yi) + (4 + 6i) = 7 - 2i[/tex]
find the value of x and y in the given equation
Lets open the parenthesis and combine like terms
Equate the real and imaginary part to solve for x and y
[tex]\left(x+4\right)+\left(y+6\right)i=7-2i\\x+4=7\\x=3\\\\y+6=-2\\y=-2-6\\y=-8[/tex]
The value of x=3 and y=-8
Now we do the same with second equation
[tex](x + yi) - (-8 + 11i) = 5 + 9i\\\\x+8+yi-11i=5+9i\\\left(x+8\right)+\left(y-11\right)i=5+9i\\x+8=5\\x=-3\\\\y-11=9\\y=9+11\\y=20[/tex]
The value of x and y is x=-3 and y=20
Learn more : brainly.com/question/18552411
The figure shows a person estimating the height of a tree by looking at the
top of the tree with a mirror. Assuming that both the person and the tree form
right angles with the ground, which of the following proportions can be used
to estimate the height of the tree
Answer:
[tex]\frac{6}{5} =\frac{x}{12}[/tex]
Step-by-step explanation:
Write a proportion in the form:
Height/side= height/side
The side lengths are 5 and 12.
The height (of the 5 side) is 6.
The proportion can be written as:
[tex]\frac{6}{5} =\frac{x}{12}[/tex]
Find the midpoint of the line segment defined by the points (1/2, -5/2) and (-4/3, -1/6)
Answer:
-5/6 and -8/3
Step-by-step explanation:
To find the cordinates of the midpoint we must add the coordinates together and divide them by 2
let A be the midpoint of this line :
A (1/2-4/3 , -5/2-1/6)
A( -5/6, -8/3)
Answer:
(-5/12 , - 4/3)Step-by-step explanation:
The midpoint of the points (1/2, -5/2) and (-4/3, -1/6) is
[tex] (\frac{ \frac{1}{2} - \frac{4}{3} }{2} \: \: \frac{ - \frac{ 5}{2} - \frac{1}{6} }{2} ) \\ \\ = ( \frac{ - \frac{5}{6} }{2} \: \: \frac{ - \frac{8}{3} }{2} ) \\ \\ = ( - \frac{5}{12} \: \: \: - \frac{4}{3} )[/tex]
(-5/12 , - 4/3)Hope this helps you
The shape on the left is transformed to the shape on the right. Figure A B C D is rotated to form figure A prime B prime C prime D prime. Which of the following statements describes the transformation? A B C D right-arrow A prime B prime C prime D prime A prime B prime C prime D prime right-arrow A B C D A B C D right-arrow D prime A prime C prime B prime D prime B prime C prime A prime right-arrow C A D B
Answer:
A
Step-by-step explanation:
I did the test and it is the only one that makes sense
Answer:
a
Step-by-step explanation:
Beginning three months from now, you want to be able to withdraw $2,300 each quarter from your back account to cover college expenses over the next four years. If the account pays .45 percent interest per quarter, how much do you need to have in your bank account today to meet your expense needs over the next four years?
Answer:
$36,450.46
Step-by-step explanation:
The amortization formula can be used to figure this. For quarterly payment A, the principal invested must be P for interest rate r and compounding n times per year for t years.
A = P(r/n)/(1 -(1 +r/n)^(-nt))
2300 = P(0.0045/4)/(1 -(1 +0.0045/4)^(-4·4))
2300 = P·0.06309934
P = 2300/0.06309934 = 36450.46
You need $36,450.46 in your account today so that you can withdraw $2300 quarterly for 4 years.
A furniture store has set aside 800 square feet to display its sofas and chairs. Each sofa utilizes 50 sq. ft. and each chair utilizes 30 sq. ft. At least five sofas and at least five chairs are to be displayed.
a. Write a mathematical model representing the store's constraints.
b. Suppose the profit on sofas is $200 and on chairs is $100. On a given day, the probability that a displayed sofa will be sold is 0.03 and that a displayed chair will be sold is 0.05. Mathematically model each of the following objectives:
1. Maximize the total pieces of furniture displayed.
2. Maximize the total expected number of daily sales.
3. Maximize the total expected daily profit.
Answer:
a) 50S + 30C ≤ 800
b) 1) MAX = S + C
2) Max = 0.03S + 0.05C
3) Max = 6S + 5C
Step-by-step explanation:
Given:
Total space = 800 square feet
Each sofa = 50 square feet
Each chair = 30 square feet
At least 5 sofas and 5 chairs are to be displayed.
a) Write a mathematical model representing the store's constraints:
Let S denote number of sofas displayed and C denote number of chairs displayed.
The mathematical model will be:
50S + 30C ≤ 800
At least 5 sofas are to be dispayed: S ≥ 5
At least 5 chairs are to be displayed: C ≥ 5
b)
1) Maximize the total pieces of furniture displayed:
S + C = MAX
2) Maximize the total expected number of daily sales:
MAX = 0.03S + 0.05C
3) Maximize the total expected daily profit:
Given:
Profit on sofas = $200
Profit on chairs = $100
Max Expected daily profit =
Max = (200S * 0.03) + (100C * 0.05)
Max = 6S + 5C
What is coefficient of the term of degree of degree 5 in the polynomial below 3x^6+5-x^2+4x^5-9 which one is the right answer A. 3 B. 4 C. 6 D. 5
Answer:
B. 4
Step-by-step explanation:
We are looking for the coefficient of the term x⁵. When we see it in the polynomial as 4x⁵, our coefficient and answer would then be 4.
Jimmy will be selling hot dogs at the football game. He bought hot dogs, buns, and condiments for a total of \$8$8dollar sign, 8 and now wants to calculate how many hot dogs he has to sell to make a profit. He graphs the profit he will make, (P)(P)left parenthesis, P, right parenthesis, as a function of the number
Answer:
the photo shows the answer ^D^ hope this helps~
Step-by-step explanation:
+also included the correct sign for confirmation xD
Answer:
up answer is correct :)
Step-by-step explanation:
Is (0,-2) a solution of 3x - y = 2?
Answer:
yes, (0,-2) is the answer when graphing this equation.
Step-by-step explanation:
Answer:
yes.
Step-by-step explanation:
the twelve inch square tiles are shipped in boxes of sixteen pieces per box. each of the boxes weighs twenty four pounds. approximately how many ounces does each tile weigh?
Answer:
1.411764706
Step-by-step explanation:
24/17=1.411764706
Given a joint PDF, f subscript X Y end subscript (x comma y )equals c x y comma space 0 less than y less than x less than 4, (1) (5 pts) Determine the constant c value such that the above joint PDF is valid. (2) (6 pts) Find P (X greater than 2 comma space Y less than 1 )(3) (9 pts) Determine the marginal PDF of X given Y
(1) Looks like the joint density is
[tex]f_{X,Y}(x,y)=\begin{cases}cxy&\text{for }0<y<x<4\\0&\text{otherwise}\end{cases}[/tex]
In order for this to be a proper density function, integrating it over its support should evaluate to 1. The support is a triangle with vertices at (0, 0), (4, 0), and (4, 4) (see attached shaded region), so the integral is
[tex]\displaystyle\int_0^4\int_y^4 cxy\,\mathrm dx\,\mathrm dy=\int_0^4\frac{cy}2(4^2-y^2)=32c=1[/tex]
[tex]\implies\boxed{c=\dfrac1{32}}[/tex]
(2) The region in which X > 2 and Y < 1 corresponds to a 2x1 rectangle (see second attached shaded region), so the desired probability is
[tex]P(X>2,Y<1)=\displaystyle\int_2^4\int_0^1\frac{xy}{32}\,\mathrm dy\,\mathrm dx=\boxed{\dfrac3{32}}[/tex]
(3) Are you supposed to find the marginal density of X, or the conditional density of X given Y?
In the first case, you simply integrate the joint density with respect to y:
[tex]f_X(x)=\displaystyle\int_{-\infty}^\infty f_{X,Y}(x,y)\,\mathrm dy=\int_0^x\frac{xy}{32}\,\mathrm dy=\begin{cases}\frac{x^3}{64}&\text{for }0<x<4\\0&\text{otherwise}\end{cases}[/tex]
In the second case, we instead first find the marginal density of Y:
[tex]f_Y(y)=\displaystyle\int_y^4\frac{xy}{32}\,\mathrm dx=\begin{cases}\frac{16y-y^3}{64}&\text{for }0<y<4\\0&\text{otherwise}\end{cases}[/tex]
Then use the marginal density to compute the conditional density of X given Y:
[tex]f_{X\mid Y}(x\mid y)=\dfrac{f_{X,Y}(x,y)}{f_Y(y)}=\begin{cases}\frac{2xy}{16y-y^3}&\text{for }y<x<4\text{ where }0<y<4\\0&\text{otherwise}\end{cases}[/tex]
Suppose a random variable X is best described by a uniform probability distribution with range 1 to 5. Find the value of that makes the following probability statements true.
a) P(X <-a)= 0.95
b) P(X
c) P(X
d) P(X ->a)= 0.89
e) P(X >a)= 0.31
Answer:
a) 4.8
b) 2.96
c) 4.4
d) 1.44
e) 3.76
Step-by-step explanation:
What we will do is solve point by point, knowing the following:
Fx (x) = P (X <= x) = (x - 1) / 4
a) P (X <-a) = 0.95
Fx (a) = 0.95
(a -1) / 4 = 0.95
a = 1 + 0.95 * 4
a = 4.8
b) P (X <a) = 0.49
Fx (a) = 0.49
(a -1) / 4 = 0.49
a = 1 + 0.49 * 4
a = 2.96
c) P (X <a) = 0.85
Fx (a) = 0.85
(a -1) / 4 = 0.55
a = 1 + 0.85 * 4
a = 4.4
d) P (X> a) = 0.89
P (X <a) = 1 - 0.89 = 0.11
Fx (a) = 0.11
(a -1) / 4 = 0.11
a = 1 + 0.11 * 4
a = 1.44
e) P (X> a) = 0.31
P (X <a) = 1 - 0.31 = 0.69
Fx (a) = 0.69
(a -1) / 4 = 0.69
a = 1 + 0.69 * 4
a = 3.76
Please help! Need Geometry help!!!!!
Answer:
938 feet
Step-by-step explanation:
b/c every angle of a rectangle is 90° u can u Pythagorean theroem to solve the question
a*a+ b*b=c*c
900*900+264*264=c*c
c=√879,696
c=938feet
Answer:
938 feet
Step-by-step explanation:
Well to solve this we need to use the Pythagorean Theorem,
[tex]a^2 + b^2 = c^2[/tex].
So we have a and b which are 900 and 264,
and we need to find c or the walking distance.
So we plug in 900 and 264 for a and b.
[tex](900)^2 + (264)^2 = c^2[/tex]
So, 900*900 = 810,000
264 * 264 = 69696
810000 + 69696 = 879696
So now we have,
879696 = c^2
To get the c by itself we do,
[tex]\sqrt{879696} = \sqrt{c}[/tex]
= c = 937.921105424
c = 938 rounded to the nearest foot
Thus,
the solution is 938.
Hope this helps :)
Dr. Hernandez is a conservation biologist studying the impacts a derelict pharmaceutical company is having on a native fish population in a nearby lake. The lake has been contaminated with bovine growth hormone and Dr. Hernandez wants to see if the fish reaching adulthood in the contaminated lake are larger than the fish in a pristine lake that is nearby. Dr. Hernandez has the weights of 30 fish from the contaminated lake and of 30 fish from the pristine lake.
Based on the experimental design of Dr. Hernandez's research and the kind of data collected, which statistical test should be used to determine whether the bovine growth hormone is increasing the growth of native fish?
A. Two-tailed two-sample t-test
B. One-tailed paired t-test
C. Two-tailed paired t-test
D. One-tailed two-sample t-test
E. One-Way ANOVA
F. Linear Regression with t-test for significance of slope
Answer:
C. Two-tailed paired t-test.
Step-by-step explanation:
Since Dr. Hernandez takes 30 samples from a contaminated lake and 30 fish from a pristine lake, he should use a two-tailed t-test.
Paired t-tests describe tests used to compare the means of two samples when each observation in one sample can be paired with an observation in the other sample. Dr. Hernandez can certainly pair the samples and observe the differences, so the answer is C. Two-tailed paired t-test.
Hope this helps!
Find the volume V of the described solid S. The base of S is a circular disk with radius 4r. Parallel cross-sections perpendicular to the base are squares.
Answer:
(1024/3)r^3.
Step-by-step explanation:
Step one: So, we have that x^2 + y^2 = 4^2 × r^2(when z component = 0) . Hence, there is the need to make y^2 the subject of the formula.
Step two: 4y^2 = 16r^2 - x^2. Where 4 ×(16r^2 - x^2) is the the cross sectional area.
Step three: the next thing to do here is to integrate the cross sectional area making 4r and -4r the upper limit and lower limit for the integration.
Step four: the integration will then give a product (16 × 64)/3 A = (1024/3)r^3.
whats 1/2 + 2/4 - 5/8?
Answer:
3/8
Step-by-step explanation:
Step 1: Find common denominators
1/2 = 4/8
2/4 = 4/8
Step 2: Evaluate
4/8 + 4/8 - 5/8
8/8 - 5/8
3/8
Alternatively, you can just plug this into a calc to evaluate and get your answer.
Answer:
3/8
Step-by-step explanation:
Look at the denominator:
2, 4, 8. The LCM (Lowest Common Multiple) is 8.
So this equation becomes
4/8+4/8-5/8=3/8
Solve the inequality a−32<1 and write the solution in interval notation, using improper fractions if necessary.
Answer:
( -∞ , 33 )
Step-by-step explanation:
To solve the inequation a-32 < 1, we need to sum on both sides 32, as:
a - 32 + 32 < 1 + 32
a < 33
It means that the solutions are all the number that are smaller than 33 or in interval notation it would be:
( -∞ , 33 )
Where 33 is not included in the interval.
3a. Write an equation in slope-intercept form of a
line that passes through (2,1) and (6,-5).
Answer:
[tex]y =- 3/2x + 4[/tex]
Step-by-step explanation:
[tex](2,1) and (6,-5).\\x_1 = 2\\x_2 = 6\\y_1 =1\\y_2 =-5\\\frac{y-y_1}{x-x_1} = \frac{y_2-y_1}{x_2-x_1}\\ \\\frac{y-1}{x-2} = \frac{-5-1}{6-2}\\\\\frac{y-1}{x-2} = \frac{-6}{4} \\Cross-Multiply\\4(y-1) = -6(x-2)\\4y-4=-6x+12\\4y =-6x+12+4\\4y = -6x+16\\Divide- through-by ; 4\\\frac{4y = -6x+16}{4} \\\\y = -\frac{3}{2} x +4[/tex]
An airplane descends during the last hour of it's flight to prepare for landing. It's altitude changes at an average of -0.15 km per minute for those 60 minutes. Write an expression to represent the total change in the airplane's elevation. ( plz answer, will give brainliest )
Answer:
-.15 km/ minute * 60 minutes
-9 km
Step-by-step explanation:
The rate is -.15 km per minute
We have 60 minutes
distance = rate times time
change in elevation is the same as the distance change
change in elevation = -.15 km/ minute * 60
change in elevation =-9 km
Answer:
(0.15 km/min) * (60 min)
Step-by-step explanation:
We see that the plane descends 0.15 kilometres every minute over the span of 60 minutes.
Use the distance-rate-time formula: d = rt, where d is the distance, r is the rate, and t is the time.
Here, our rate is r = 0.15 km/min and our time is t = 60 minutes. Then the total change in elevation is:
d = rt
d = 0.15 * 60 = 9 km
Note that we disregard the negative sign from -0.15 km/min because the question is asking for the change in elevation. Change is never a negative value.
Hence, the expression will be: 0.15 * 60, which simplifies to 9 km.
~ an aesthetics lover
Consider the following function. f(x) = 2x + 5. Place the steps for finding f-1 (x) in the correct order. A. x-2/5= y B. y = 2x + 5 C. y-5 = 2x D. X-5/2=y E. f-1(x) = x-5/2 F.x= 2y+ 5 G. x-5= 2y H. f-1(x) = x-2/5
Answer:
[tex]\boxed{\sf \ \ f^{-1}(x)=\dfrac{x-5}{2} \ \ }[/tex]
Step-by-step explanation:
hello,
the easiest way to understand what we have to do is the following in my opinion
we can write
[tex](fof^{-1})(x)=x\\<=>f(f^{-1}(x))=x\\<=>2f^{-1}(x)+5=x\\<=>2f^{-1}(x)+5-5=x-5 \ \ \ subtract \ \ 5\\<=> 2f^{-1}(x)=x-5 \\<=> f^{-1}(x)=\dfrac{x-5}{2} \ \ \ divide \ by \ 2\\[/tex]
so to follow the pattern of your question
y = 2x + 5
we need to find x as a function of y, so let's swap x and y
x = 2y + 5
then subtract 5
x - 5 = 2y
then divide by 2
[tex]\dfrac{x-5}{2}=y[/tex]
finally
[tex]f^{-1}(x)=\dfrac{x-5}{2} \\[/tex]
hope this helps
Answer:
1. y= 2x + 5
2. x = 2y + 5
3. x - 5 = 2y
4. (x-5)/2 =u
5. f^-1(x) = (x-5)/2
Step-by-step explanation:
:)
Please Help! Select the correct answer. Simon used these steps to solve an equation:
Answer:
A.
Step-by-step explanation:
From Step 3 to Step 4, Simon added -42 to both sides.
This is the addition property of equality: as long as you add the same thing to both sides, the equation remains equal.
A.