Hello, I need help with an equation
i did it, but it looks like it needs revision
• A teacher is looking for the best option in purchasing school supplies for a classroom. Company A is offering a discount for every dollar amount spent; Company B is offering a higher discount than Company A, but the discount is applicable only for every dollar amount spent above $20. Determine which company will offer a better price based upon the dollar amount the teacher spends on school supplies.

- anonymous

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- anonymous

do you have a formula for determining the cost of each company? If you don't, develop a formula for each company, and then I can help you from there

- anonymous

yes i do
there are three separate formulas
y=0.8x
y=0.7x+6 and y=x

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- anonymous

I am having trouble with the excel graph, and i don't know if something is just not adding up

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- anonymous

I'm not sure what those equations correspond to

- anonymous

well, the discounts are 20% from Company A based on any amount purchased, and 30% from Company B for supplies purchased above $20.

- anonymous

ok, so when for the second one, when x is 20, y is twenty, and afterwards y = (x -20) * .7

- anonymous

sorry, y = (x - 20) * .7 + 20

- anonymous

yes
but how do I put it in a graph? how do I find my points for those 3 equations? I attached an excel graph, but something isn't accurate

- anonymous

sorry, i can't open up the excel graph. but to solve the problem, you solve for the two equations i posted above

- anonymous

did you use scatter plot instead of line graph?

- anonymous

go to where you change chart type, and choose the segmented line, instead of the smooth curve under scatter plot

- anonymous

in the scatter chart?

- anonymous

Can I put any numbers to solve the equation, or how would I solve this equations above?

- anonymous

you see how two of the equations intersect on the graph?

- anonymous

yes, at 60, but at the bottom, i have a bump

- anonymous

these are the points that I use, 0, 20,40, 60,80

- anonymous

at x = 20, it will be discontinuous. it's supposed to be

- anonymous

x1 y1 x2 y2
0 0 0 0
20 16 20 20
40 32 30 27
60 48 40 34
80 64 60 48

- anonymous

i think something is wrong with the points that I'm using

- anonymous

use the equations i gave then

- anonymous

Are they the same as y=0.8x and 0.7x+6? Or can you regive me your equations if they are different?

- anonymous

why is it six and not 34? from 0 - 20, the equations should be y = .8 * x and y = x, after 20, it should be y = .8 x and y = .7 * x + 34

- anonymous

you know what, nevermind, the equation is right, i added 14 + 20 instead of subtracted

- anonymous

so your equations are correct

- anonymous

Whew, a relief since I have been working on them since yesterday. But my question is, what points do I use to plot the graph? How do I solve the equations?

- anonymous

I'm like math illiterate, which is probably why you're wondering why I'm having a hard time with these equations.

- anonymous

your points are correct, it shows exactly where the two graphs are equal. the only problem is, you chose to have the graph smooth the lines, instead of jagged. make them jagged

- anonymous

you see where it's curvy? it should just be an angle

- anonymous

how do I make them jagged? and do I need to do a point for the equation y=x

- anonymous

no, read up top, you need to change the graph type

- anonymous

look in excel where it has the types, where one is curved, and the other is jaggedy

- anonymous

So you can see my graph in front of you, does it make sense to you with both companies?

- anonymous

yes, it's fine, except that it's curved, and not jaggedy

- anonymous

in my excel, if i right click on the graph, and go to CHANGE CHART TYPE, i have the option on the bottom of the window to change it to a jagged scatter plot. other than that, it's supposed to have them cross like that, and the one is supposed to slightly change direction

- anonymous

Ok and how do I simultaneously solve those 3 equations?

- anonymous

you don't simultaneously solve all three

- anonymous

only the two, after x > 20

- anonymous

ok and how do I solve those 2? I'm sorry if I sound clueless, but I just don't understand math

- anonymous

you see how you have them already solved for y? you just set the right side of the one to the right side of the other, as in .8x = .7x+6, and solve for x

- anonymous

ok let me try that

- anonymous

x=60?

- anonymous

Would I be able to attach the file for the word problem so you can see if I did it right?

- anonymous

no, you did that right, but your answer doesn't match your data

- anonymous

so how do I fix it?

- anonymous

wait, is that your x or your y?
your x is 60, and your y is 48?

- anonymous

yes

- anonymous

then you're done

- anonymous

So the equations with the graph are accurate?

- anonymous

This is what it asks for?

- anonymous

3. Solve the system of linear equations algebraically using either the substitution method or the elimination method to determine where the two cost options are equivalent, showing all work.
a. Explain each step used to solve the system of linear equations. Include the following in your explanation:
• The algebraic method used to solve the system of equations
• All mathematical operations used to solve the system of equations
• The solution of the system of equations

- anonymous

Which method did I use?

- anonymous

substitution

- anonymous

How did you come up with all three equations?

- anonymous

Are you there?

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