Answer:
19.45
Step-by-step explanation:
The median is the middle number. Put the data in order from smallest to largest
16.3, 17.8,17.8 ,18.0, 18.7,19.3, 19.6,20.1,20.5, 21.9, 25.2 ,25.4
There are 12 pieces of data,
16.3, 17.8,17.8 ,18.0, 18.7,19.3, 19.6,20.1,20.5, 21.9, 25.2 ,25.4
The median lies between the 6th and 7th piece
Add the 6th and 7th together and divide by 2
(19.3+19.6)/2 =19.45
Answer:
[tex]\large \boxed{\mathrm{19.45}}[/tex]
Step-by-step explanation:
Median of a data set is the middle value.
The data is to be arranged from smallest to largest.
16.3, 17.8, 17.8, 18.0, 18.7, 19.3, 19.6, 20.1, 20.5, 21.9, 25.2, 25.4
Find the middle value.
16.3, 17.8, 17.8, 18.0, 18.7, 19.3, 19.6, 20.1, 20.5, 21.9, 25.2, 25.4
Average the two middle numbers.
(19.3+19.6)/2 = 19.45
The median of the data set is 19.45.
. Use the quadratic formula to solve each quadratic real equation. Round
your answers to two decimal places. If there is no real solution, say so.
a) x^2 - 5x + 11 = 0
b) -2x^2 - 7x + 15 = 0
c) 4x^2 - 44x + 121 = 0
Answer:
A. No real solution
B. 5 and -1.5
C. 5.5
Step-by-step explanation:
The quadratic formula is:
[tex]\begin{array}{*{20}c} {\frac{{ - b \pm \sqrt {b^2 - 4ac} }}{{2a}}} \end{array}[/tex], with a being the x² term, b being the x term, and c being the constant.
Let's solve for a.
[tex]\begin{array}{*{20}c} {\frac{{ 5 \pm \sqrt {5^2 - 4\cdot1\cdot11} }}{{2\cdot1}}} \end{array}[/tex]
[tex]\begin{array}{*{20}c} {\frac{{ 5 \pm \sqrt {25 - 44} }}{{2}}} \end{array}[/tex]
[tex]\begin{array}{*{20}c} {\frac{{ 5 \pm \sqrt {-19} }}{{2}}} \end{array}[/tex]
We can't take the square root of a negative number, so A has no real solution.
Let's do B now.
[tex]\begin{array}{*{20}c} {\frac{{ 7 \pm \sqrt {7^2 - 4\cdot-2\cdot15} }}{{2\cdot-2}}} \end{array}[/tex]
[tex]\begin{array}{*{20}c} {\frac{{ 7 \pm \sqrt {49 + 120} }}{{-4}}} \end{array}[/tex]
[tex]\begin{array}{*{20}c} {\frac{{ 7 \pm \sqrt {169} }}{{-4}}} \end{array}[/tex]
[tex]\begin{array}{*{20}c} {\frac{{ 7 \pm 13 }}{{-4}}} \end{array}[/tex]
[tex]\frac{7+13}{4} = 5\\\frac{7-13}{4}=-1.5[/tex]
So B has two solutions of 5 and -1.5.
Now to C!
[tex]\begin{array}{*{20}c} {\frac{{ -(-44) \pm \sqrt {-44^2 - 4\cdot4\cdot121} }}{{2\cdot4}}} \end{array}[/tex]
[tex]\begin{array}{*{20}c} {\frac{{ 44 \pm \sqrt {1936 - 1936} }}{{8}}} \end{array}[/tex]
[tex]\begin{array}{*{20}c} {\frac{{ 44 \pm 0}}{{8}}} \end{array}[/tex]
[tex]\frac{44}{8} = 5.5[/tex]
So c has one solution: 5.5
Hope this helped (and I'm sorry I'm late!)
Helppp meeeew pleaseeeee
Answer:
Hey there!
1 1/10=1.1
2/25=0.08
Each serving requires 0.08 kg, and he has 1.1 kg.
Thus, he can make 1.1/0.08, or 13.75 servings.
Let me know if this helps :)
Answer:
13 servings of tofu dish.
Step-by-step explanation:
First, convert the fractions to decimal numbers:
1 1/10 kg = 0.1 kg
2/25 kg = 0.08 kg
Now find how many servings of tofu dish will cover 0.1 kg of tofu:
2/25 kg = 1 serving
1 1/10 kg = ?
= 1 1/10 ÷ 2/25 kg
= 11/10 × 25/2
= 55/4
= 13.75 servings
Approximate it to a whole number:
13 servings.
What is the formula for a^3-b^3??
Answer:
[tex]\boxed{\mathrm{view \ explanation}}[/tex]
Step-by-step explanation:
The difference of two cubes formula is given as:
[tex]a^3-b^3 =(a-b)(a^2 +ab+b^2)[/tex]
Step-by-step explanation:
[tex] {(a - b)}^{3} = {(a - b)}^{2} (a - b)[/tex]
[tex] {a}^{3} - 3{a}^{2} b + 3a {b}^{2} - {b}^{3} = {(a - b)}^{2} (a - b)[/tex]
[tex] {a}^{3} - {b}^{3} + 3ab(a - b)= {(a - b)}^{2} (a - b)[/tex]
[tex] {a}^{3} - {b}^{3}= {(a - b)}^{2} (a - b) + 3ab(a - b)[/tex]
[tex] {a}^{3} - {b}^{3} = (a - b)(( {a}^{2} - 2ab + {b}^{2} ) - 3ab)[/tex]
[tex] {a}^{3} - {b}^{3} = (a - b)( {a}^{2} + ab + {b}^{2} )[/tex]
Is the product of two irrational numbers always an irrational number?
Answer:
Step-by-step explanation:
Not always.
√3 * √27 = √81 = 9
What is m
Round the answer to the nearest whole number.
O 30°
O 35°
O 55°
O 60°
Answer:
30
Step-by-step explanation:
fufyfuf7fjcjcufuy7fufucyyxyvkbuvufudydy shut up
The dosage for a certain drug calls for 20mg per kg per day and is divided into two doses(1every 12 hours) if a person weighs 197 pounds how much of the drug should be given each dose
Answer:
893.42
Step-by-step explanation:
1kg=2.205pounds
so 20mg is for 2.205pounds
therefore for 197pounds will be 1784.84mg
but the dose is once every 12hrs meaning twice a day so divide 1784.84/2 to get the pounds
hat is the solution of the system of equations?
y = 3x – 4
−3y = −9x + 12
what equation accurately represent this statement three less than 4 times a number is less than 12
Answer: 4t - 3 < 12
Step-by-step explanation:
Wo commondities A and B cost 070 and D80 respe
with 26 kg of B and the mixture issold at 085 per kg: calo
The weight (in kg) of 50 contenstants at a competition is
65 66 67 66 64 66 65 63 65 68
64 62 66 64 67 65 64 66 65 67
65 67 66 64 65 64 66 65 64 65
66 65 64 65 63 63 67 65 63 64
66 64 68 65 63 65 64 67 66 64
a. construct a frequency table for the discrete data
b. calculate, correct to 2 decimal places, the
mean,
ii. standard deviation of the data
Answer:
b) 65.08
ii) 0.75
Step-by-step explanation:
x(Kg): 62 63 64 65 66 67 68
Frequency(f): 1 5 11 15 10 6 2
xf: 62 315 704 975 660 402 136
b) mean(X) = ∑xf/N = 3254/50 = 65.08
c) x - X : -3.08 -2.08 -1.08 -0.08 0.92 1.92 2.92
(x - X)²: 9.49 4.33 1.17 0.0064 0.85 3.69 8.53
ii) Standard deviation(S.D.): √(∑(x - X)²/N = √(28.0664)/50 = √0.5613
∴ S.D.= 0.75
A zucchini plant in Darnell’s garden was 10 centimeters tall when it was first planted. Since then, it has grown approximately 0.5 centimeter per day. a. Write a rule to describe the function. b. After how many days will the zucchini plant be 18.5 centimeters tall?
Answer:The number of days it will grow to be 18.5 cm tall is 17 days.
Step-by-step explanation:
To find how many days it will grow until it reaches 18.5 centimeters, first find the difference of the new height by the old height.
So= 18.5-10= 8.5cm
8.5 is the centimeters it needs to grow to be 18.5 cm tall.
Then, divide it by the number of centimeters it will grow in one day, which is 0.5, to find the days it grew 8.5 cm.
So= 8.5÷0.5= 17
I hope this helps! Ask me if you're confused.
-3=n/2-6 help pleaseeee!!!!
Answer:
6 = n
Step-by-step explanation:
-3=n/2-6
Add 6 to each side
-3+6 = n/2 -6+6
3 = n/2
Multiply each side by 2
3*2 = n/2 *2
6 = n
━━━━━━━☆☆━━━━━━━
▹ Answer
n = 6
▹ Step-by-Step Explanation
-3 = n/2 - 6
Multiply both sides by 2:
-6 = n - 12
Rearrange the terms:
-n -6 = -12
Calculate:
-n = -6
Change the signs:
n = 6
Hope this helps!
CloutAnswers ❁
━━━━━━━☆☆━━━━━━━
-7p+2(5p-8)=6(p+6)-7
Answer:
-15
Step-by-step explanation:
-7p+10p-16=6p+36-7
3p-16=6p+29
3p-6p=29+16
-3p=45
p=45/-3
p=-15
The research chemists at MegaClean created a new cleaner that keeps car and truck tires shiny and clean for one year. They believe that this product will be highly successful and will attract customers to purchase their existing line of household cleaning products.
Answer:
Complementary effect
Step-by-step explanation:
Complementary goods service is another good or item used in conjunction with the service. In general, complementary goodness does not matter when eaten alone, but when combined with another good or service, it increases the overall value of the offering. When a product shares a lucrative relationship with another product offering it is considered an affiliate, for example, an iPhone and apps used with it, so that this is good example of Complementary effectPlease help me!! I'll give brainliest btw
Answer:
e. cannot be determined
Step-by-step explanation:
m = 1/2( x + x + 10) = 1/2(2x + 10) = x + 5
n = 1/2(x² + x + 10) =
m/n = (x+5)/(1/2(x² + x + 10))
Not enough information
When dividing polynomials using factorization, canceling identical factors in the denominator and the numerator will give the _______.
Answer:
quotient
Step-by-step explanation:
Answer:
quotient
Step-by-step explanation:
Cancelling identical factors in the numerator and the denominator will give the quotient. For example,x2+5x+6x+3=(x+2)(x+3)x+3 = x + 3
What is the y−intercept of the line that passes through the point (4,9)and is parallel to the line y=12x+2?
Answer:
y- intercept = - 39
Step-by-step explanation:
The equation of a line in slope- intercept form is
y = mx + c ( m is the slope and c the y- intercept )
y = 12x + 2 ← is in slope- intercept form
with slope m = 12
Parallel lines have equal slopes, thus
y = mx + c ← is the partial equation
To find c substitute (4, 9) into the partial equation
9 = 48 + c ⇒ c = 9 - 48 = - 39 ← y- intercept
Answer:
y-intercept = -39
Step-by-step explanation:
if two lines are parallel it means they have the same gradient so we compare the equation given to the default equation of a line
y=mx+c
y=12x+2
comparing we have the gradient m=12 now finding the equation of the line parallel to the given line we use
y-y1=m(x-x1)
y1=9 and x1=4
y-9=12(x-4)
y-9=12x-48
y=2x-48+9
y=2x-39
comparing to the default equation of a line y=mx+c where c is the y-intercept
therefore the y-intercept is -39
We want to build a swimming pool that is 2m by 6m. On our page it measured out to be 8cm by 24cm. What is tge scale that can be used
Answer:
1:25
Step-by-step explanation:
Given
Dimensions of swimming pool:
W = 2 mL = 6 mDimensions on paper:
w = 8 cml = 24 cmScale is the ratio of same measurements:
w/W = 8 cm/2 m = 8 cm / 200 cm = 1/25So the scale is 1:25
Please answer this question now
Answer:
54
Step-by-step explanation:
To solve problems like this, always recall the "Two-Tangent theorem", which states that two tangents of a circle are congruent if they meet at an external point outside the circle.
The perimeter of the given triangle = IK + KM + MI
IK = IJ + JK = 13
KM = KL + LM = ?
MI = MN + NI ?
Let's find the length of each tangents.
NI = IJ = 5 (tangents from external point I)
JK = IK - IJ = 13 - 5 = 8
JK = KL = 8 (Tangents from external point K)
LM = MN = 14 (Tangents from external point M)
Thus,
IK = IJ + JK = 5 + 8 = 13
KM = KL + LM = 8 + 14 = 22
MI = MN + NI = 14 + 5 = 19
Perimeter = IK + KM + MI = 13 + 22 + 19 = 54
Henry gathered data about the types of nuts in five handfuls of mixed nuts. The data he gathered is shown in the table. Select the points that represent this data.
Answer:
Look below.
Step-by-step explanation:
The location of the coordinate plane will be shown in the graph.
What is coordinate geometry?Coordinate geometry is the study of geometry using the points in space.
Henry gathered data about the types of nuts in five handfuls of mixed nuts.
The data he gathered is shown in the table.
Handful Number of peanuts Number of other nuts
A 9 7
B 6 5
C 8 9
D 5 7
E 7 4
The graph is shown below.
More about the coordinate geometry link is given below.
https://brainly.com/question/1601567
#SPJ2
A piece of blue yarn is 5/ 3/7 yards long. A piece of pink yarn is 5 times as long as the blue yarn. How much longer is the pink yarn than the blue yarn?
Answer:
27 1/7
Step-by-step explanation:
Multiply 5×5=25 and afterwards multiply 3/7×5=2 1/7
which inequality is graphed on the coordinate plane?
Answer:
a
Step-by-step explanation:
1:cancel out any answers with equal to since the line is dotted
2:pick any two points of your choice and work out the gradient
3:use the gradient a point on the line and an anonymous point (x,y) to get equation of a line
4:then choose a point (0,0) and substitute x with 0 in the equation to get y (in this case it's -1) which is less than 0 hope it helps
The inequality that is graphed on the coordinate plane is y ≤ [tex]x^{2}[/tex].
The graph of this inequality is a parabola that is facing downwards. The parabola opens downwards because the inequality symbol is less than or equal to (≤). The vertex of the parabola is at the point (0, 0).
The parabola intersects the x-axis at the points (-1, 1) and (1, 1). This means that the values of x that satisfy the inequality are all the values that are less than or equal to 1.
The parabola does not touch the x-axis at any other points, so the values of x that do not satisfy the inequality are all the values that are greater than 1.
Here is a graph of the inequality y ≤ [tex]x^{2}[/tex]:
parabola that is facing downwards and intersects the x-axis at (-1, 1) and (1, 1)Opens in a new window
www.teachoo.com
parabola that is facing downwards and intersects the x-axis at (-1, 1) and (1, 1)
The other inequalities that are shown in the answer choices are not graphed correctly. The inequality y ≥ [tex]x^{2}[/tex] is graphed as a parabola that is facing upwards. The inequality y = [tex]x^{2}[/tex] is graphed as a line that is not a parabola. The inequality y > [tex]x^{2}[/tex] is not graphed at all.
Therefore, the only inequality that is graphed correctly is y ≤ [tex]x^{2}[/tex].
Learn more about inequality here: brainly.com/question/20383699
#SPJ2
What is the slope of the line containing the midpoint of the segment with endpoints at (2, 4) and (0, -2) and the midpoint of the segment with endpoints at (5, 1) and (1, 5)?Express your answer in simplest form. Plzzzz help!!!!
Answer:
slope = 1
Step-by-step explanation:
midpoint of (2, 4) and (0, -2)
(2 + 0)/2 = 1 and (4 + -2)/2 = 1
(1, 1)
midpoint of (5, 1) and (1, 5)
(5 + 1)/2 = 3 and (1 + 5)/2 = 3
(3, 3)
slope = (3-1)/(3-1) = 2/2 = 1
What are all of the properties of kites? This is an inquiry comprised within the means of 'high school' 'geometry'.
[tex] \Large{ \boxed{ \rm{ \red{Refer \: to \: the \: attachment}}}}[/tex]
It is a quadrilateral in which two pairs of adjacent sides are equal in measure.➤ Like Here, AB = BC and AD = CD
The diagonals intersect at right angles. Here, OA = OC and angle A = angle CDiagonals bisect the touching angles. Like here, Diagonal BD intersects angle B and angle D.Diagonal BD divides the kite into two congurent triangles of equal area. So, these triangles can overlap each other.━━━━━━━━━━━━━━━━━━━━
I am on a farm with pigs and horses. The ratio of pigs to horses is 4:1. The ratio of adult pigs to piglets is 1:5. The ratio of adult horse to foal is 3:1. What fraction of the farm are babies (foals and piglets)?
Answer:
EAT THIS ANDAD Which polynomial has (3x + 2) as a binomial factor?
6x3 + 3x2 + 4x + 2
12x2 + 15x + 8x + 10
18x3 – 12x2 + 9x – 6
21x4 + 7x3 + 6x + 2
Step-by-step explanation:
a second degree equation in one variable example how many solutions does it have ?a second degree equation in one variable example how many solutions does it have ? is it possible to have many solutions or no solutions tions give an example for each
Answer:
0, 1, or 2 real solutions
Step-by-step explanation:
Including complex and repeated solutions, a polynomial with real coefficients, and of degree n, always has n solutions.
If you're only concerned about real solutions, a 2nd degree equation in one variable may have 0, 1, or 2 real solutions. Here are some examples.
0 solutions: x^2 +1 = 01 solution: x^2 = 02 solutions: x^2 -1 = 0**Yoxelt buys 4 1/2 gallons of soda. One-fourth of the soda he bought was Pepsi and the rest was Sprite. How many gallons of Pepsi did Yoxelt buy? Show all work below.
Answer:
1 1/8
Step-by-step explanation:
1/4 of the 4 1/2 gallons were Pepsi, so the amount is ...
(1/4)(9/2) = (1·9)/(4·2) = 9/8 = 1 1/8
Yoxelt bought 1 1/8 gallons of Pepsi.
PLEASE HELP ME Answer the following two questions in your own words: 1. Why can I divide instead of distribute? Why is that allowed? Ex. why can I divide by 6 in 6(3x + 4) = 12 instead of distribute the 6? 2. When creating common denominators, why do I have to multiply the numerator AND the denominator? Ex. why do I have to multiply 1 by 5 AND 2 by 5 when adding 1/2 + 3/10?
Answer:
1. You can divide both sides of an equation by any number except zero. If dividing both sides simplifies the equation, then it's better to do than than to distribute.
2. A fraction can be thought of as a ratio. To keep the value of the fraction the same, you must multiply or divide the numerator and denominator by the same number. If you multiply only the denominator by a number, the value of the fraction changes.
Step-by-step explanation:
1.
6(3x + 4) = 12
Since the goal in solving this equation is to isolate x, meaning you want x alone on the left side, you need to do whatever legal operations that will accomplish that. Since 6 is a factor and (3x + 4) is a factor in a multiplication, you can divide both sides by 6 simplifying the left side. It is also correct to distribute on the left side, but it will make the solution longer.
Method 1: start by dividing both sides by 6
6(3x + 4) = 12
Step 1: Divide both sides by 6
3x + 4 = 2
Step 2: Subtract 4 from both sides
3x = -2
Step 3: Divide both sides by 3
x = -2/3
Method 2: start by distributing on the left side
6(3x + 4) = 12
Step 1: distribute the 6 on the left side
18x + 24 = 12
Step 2: subtract 24 from both sides
18x = -12
Step 3: divide both sides by 18
x = -12/18
Step 4: reduce the fraction
x = -2/3
As you can see, the solution is the same. The only difference is one extra step with the reduction of the fraction in the case of distributing the 6.
2.
This has to do with the meaning of fractions.
For example, take the fraction 1/2.
This fraction means that you divided the unit into 2 equal parts, shown by the denominator of 2. Then you are taking 1 of those parts, shown by the numerator of 1. 1/2 means 1 out of 2. You can also think of 1/2 as the ratio of 1 to 2.
To add and subtract two factions, we need a common denominator. That means we must rewrite one or both fractions being added or subtracted in a way that they both have the same denominator. We need the fractions to represent the same amounts they did originally. If you changed only the denominator, you'd be changing the actual value of the fraction.
You need to add 1/2 and 3/10.
The least common denominator of 2 and 10 is 10, so we need to have both fractions with a denominator of 10. 3/10 already has a denominator of 10, so we just need to change 1/2 to a fraction with 10 in the denominator. By multiplying 2 by 5 we get 10, so we need to multiply the denominator of 1/2 by 5 to end up with a denominator of 10.
1/2 + 3/10
If you only changed the denominator of 1/2 to 10 by multiplying 2 * 5 = 10, you'd end up with
1/10 + 3/10,
but now think of the fraction 1/10 and compare it to 1/2.
1/2 means divide the unit into 2 equal parts and take 1 part.
1/10 means divide the unit into 10 equal arts and take 1 part.
1/2 is not the same as 1/10, so rewriting the addition
1/2 + 3/10 as 1/10 + 3/10 is actually changing the problem.
Now see what happens when we multiply both the numerator and denominator by the same number, in this case 5.
We change 1/2 to (1 * 5)/(2 * 5) = 5/10. 1/2 equals 5/10. If you divide a unit into 10 equal parts and you take 5 parts, you have taken the same number of parts as if you had divided the unit into 2 parts and taken 1 part.
In other words, 1/2 is exactly the same amount as 5/10. The only difference between 1/2 and 5/10 is the way they are written.
Now we can correctly continue with the addition:
1/2 + 3/10 = 5/10 + 3/10 = 8/10
Finally we reduce 8/10 to 4/5 by dividing both the numerator and denominator by 4.
Could anyone help me with number 25 THANK YOU!!!
Answer:
ΔABC ~ ΔQPR by the Angle-Angle (AA) similarity theorem of two triangles
Step-by-step explanation:
The coordinates of the vertices are given as follows;
A = (1, 2), B =(9, 8), C = (1, 8)
P= (5, -3), Q = (-7, 6), R = (-7, -3)
The given dimensions of AB and PQ are 10, and 15 respectively
The, l lengths of the sides of triangles are found as follows;
[tex]l = \sqrt{\left (y_{2}-y_{1} \right )^{2}+\left (x_{2}-x_{1} \right )^{2}}[/tex]
For segment BC, we have;
B =(9, 8), C = (1, 8)
(x₁, y₁) = (9, 8), (x₂, y₂) = (1, 8), substituting gives;
Length BC = 8
For length CA, C = (1, 8) A = (1, 2)
(x₁, y₁) = (1, 8)
(x₂, y₂) = (1, 2)
The length found by substituting the values for (x₁, y₁), (x₂, y₂) in the length equation gives; Length CA = 6
Given that length CA² + BC² = 8² + 6² = 64 + 36 = 100 = BA², we have by Pythagoras theorem, we have ΔABC is a right triangle
Similarly, for ΔQPR, we have;
Length QR, Q = (-7, 6), R = (-7, -3) = 9
Length PR, P= (5, -3), R = (-7, -3) = 12
QR² + PR² = 9² + 12² = 225 = 15² = PQ²
∴ ΔQPR is a right triangle
By comparing the ratio of the sides, we have;
cos(θ) = PR/PQ = 12/15 = 4/5, θ = cos⁻¹(4/5) = 36.9°
∠RPQ = 36.9°
sin(θ) = QR/PQ = 9/15 = 3/5
Similarly in triangle ΔABC, we have;
cos(θ) = BC/AB = 8/10 = 4/5
∠CBA = 36.9°
Therefore, ∠CBA ≅ ∠RPQ = 36.9°
Also ∠PRQ ≅ ∠BCA = 90° (Angle opposite hypotenuse side of right triangle
Therefore, ΔABC and ΔQPR are similar triangles by the Angle-Angle (AA) similarity theorem of two triangles.
Please answer this question now
Answer:
30.9 cm²
Step-by-step explanation:
To find the surface area of this figure, we find the area of the base and the 3 identical sides.
The base is split into two identical right triangles. Let's find the area of one and multiply by two.
Half of 3: 1.5
[tex]1.5\cdot2.6=3.9\\3.9\div2=1.95[/tex]
There are two right triangles:
[tex]1.95\cdot2=3.9[/tex]
The area of one of the sides will be the same thing, except the height is 6.
[tex]1.5\cdot6=9\\9\div2=4.5\\4.5\cdot2=9[/tex]
There are 3 sides identical to this one:
[tex]9\cdot3=27[/tex].
Add 27 and 3.9:
[tex]27+3.9=30.9[/tex]
Hope this helped!
Answer:
30.9 square centimeters
Step-by-step explanation:
3 * 1/2(3)(6) + 1/2(3)(2.6) = 30.9
1. The cost of buying some books is partly constant and partly varies with the number of books bought. The cost is #4800 when 20 books are bought and #8000 when 40 are bought. Find the cost when 1000 books are bought
Answer:
Step-by-step explanation:
let the cost based on number of book bought be x and the constant be c:
4800 = 20x + c
8000 = 40x + c
c is common in both equations:
c =4800-20x
c = 8000-40x
equate the two:
4800-20x = 8000 - 40x
20x = 3200
x = 160
and c = 4800-20*160
c = 1600
Cost of 1000 books:
160*1000 + 1600
= 161600