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Irina18 [472]
1 year ago
13

Amanda and Mofor are selling wrapping paper for a school fundraiser. Customers can buy rolls of plain wrapping paper and rolls o

f holiday wrapping paper. Amanda sold 13 rolls of plain wrapping paper and 12 rolls of holiday wrapping paper for a total of $208. Mofor sold 4 rolls of plain wrapping paper and 3 rolls of holiday wrapping paper for a total of $55. Fine the cost of one roll of plain wrapping paper and one roll of holiday wrapping paper.
Mathematics
1 answer:
Lostsunrise [7]1 year ago
8 0

Given:

Amanda sold 13 rolls of plain wrapping paper and 12 rolls of holiday wrapping paper for a total of $208.

And,

Mofor sold 4 rolls of plain wrapping paper and 3 rolls of holiday wrapping paper for a total of $55.

Let, x be the cost of one roll of plain wrapping paper and y be the cost of one roll of holiday wrapping paper.

The equations are,

\begin{gathered} 13x+12y=208\ldots\ldots\ldots\text{.....}(1) \\ 4x+3y=55\ldots\ldots..\ldots\ldots\ldots\text{.}(2) \end{gathered}

Solve the equations,

\begin{gathered} 4x+3y=55 \\ 4x=55-3y \\ x=\frac{55-3y}{4} \\ \text{Put it in quation (1)} \\ 13x+12y=208 \\ 13(\frac{55-3y}{4})+12y=208 \\ \frac{715-39y}{4}+12y=208 \\ 715-39y+4(12y)=4(208) \\ 715-39y+48y=832 \\ 9y=832-715 \\ 9y=117 \\ y=\frac{117}{9} \\ y=13 \end{gathered}

Put the value of y in equation (2),

\begin{gathered} 4x+3y=55 \\ 4x+3(13)=55 \\ 4x+39=55 \\ 4x=55-39 \\ 4x=16 \\ x=\frac{16}{4} \\ x=4 \end{gathered}

Answer:

The cost of one roll of plain wrapping paper is x = $4.

The cost of one roll of holiday wrapping paper is y = $13.

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Answer:

So the approximate relative minimum is (0.4,-58.5).

Step-by-step explanation:

Ok this is a calculus approach.  You have to let me know if you want this done another way.

Here are some rules I'm going to use:

(f+g)'=f'+g'       (Sum rule)

(cf)'=c(f)'          (Constant multiple rule)

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12x^2+26x-12=0

Divide both sides by 2:

6x^2+13x-6=0

Compaer 6x^2+13x-6=0 to ax^2+bx+c=0 to determine the values for a=6,b=13,c=-6.

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c=-6

We are going to use the quadratic formula to solve for our critical numbers, x.

x=\frac{-b \pm \sqrt{b^2-4ac}}{2a}

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Let's separate the choices:

x=\frac{-13+\sqrt{313}}{12} \text{ or } \frac{-13-\sqrt{313}}{12}

Let's approximate both of these:

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This is a cubic function with leading coefficient 4 and 4 is positive so we know the left and right behavior of the function. The left hand side goes to negative infinity while the right hand side goes to positive infinity. So the maximum is going to occur at the earlier x while the minimum will occur at the later x.

The relative maximum is at approximately -2.5576505.

So the relative minimum is at approximate 0.3909838.

We could also verify this with more calculus of course.

Let's find the second derivative.

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f''(x)=24x+26

So if f''(a) is positive then we have a minimum at x=a.

If f''(a) is negative then we have a maximum at x=a.

Rounding to nearest tenths here:  x=-2.6 and x=.4

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So we have a minimum at x=.4.

Now let's find the corresponding y-value for our relative minimum point since that would complete your question.

We are going to use the equation that relates x and y.

I'm going to use 0.3909838 instead of .4 just so we can be closer to the correct y value.

y=4(0.3909838)^3+13(0.3909838)^2-12(0.3909838)-56

I'm shoving this into a calculator:

y=-58.4654411

So the approximate relative minimum is (0.4,-58.5).

If you graph y=4x^3+13x^2-12x-56 you should see the graph taking a dip at this point.

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