Author Topic: Math Help : System of linear equations. :C (Read 602 times)

SlayerZ99 · October 10, 2011, 05:31:05 PM

Im doing these problems and the directions are "For each problem, first create a system of linear equations, and then solve the system to answer the questions"
I think I'm getting the right answer but I dont know how to make a system of linear equation.
First Problem "
"A pharmacist has two bottles of saline solution on her shelf. One bottle is at a strength of 2% and the second is at 10%. If she wished to create 100 ml of an 8% solution, how much of each bottle should she use?"

I got 25ml of 2% and 75ml of 10%

Help please :C

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SlayerZ99 · October 10, 2011, 05:41:13 PM

hi :C

TheChaosCarrier · October 10, 2011, 05:45:22 PM

pretty sure that's the correct answer.
but the point of this is how you found the answer, besides looking in the back of the book like a cheating cigarette.

post your equations and we can help you to better understand Algebra.
especially since most of the people here are in highschool still and most likely take algebra/advanced algebra in 9th/10th grade.

SlayerZ99 · October 10, 2011, 05:49:16 PM

How I did it
Took the total -> 100%
Randomly divided; I started at 50% and 50%
Did

50*.02 + 50*.1 = .8

and if the answer was to high I would lower the percent for the 10% and if it was too low I would raise the percent for the 10%

TheChaosCarrier · October 10, 2011, 05:54:19 PM

i think you're doing this wrong, but found the correct answer in a different way.
http://en.wikipedia.org/wiki/System_of_linear_equations
nowadays HS math books do a terrible job at explaining this stuff.

SlayerZ99 · October 10, 2011, 06:04:44 PM

I just need to figure out the equations now.

Headcrab Zombie · October 10, 2011, 06:13:35 PM

Quote from: SlayerZ99 on October 10, 2011, 05:49:16 PM

How I did it
Took the total -> 100%
Randomly divided; I started at 50% and 50%
Did

50*.02 + 50*.1 = .8

and if the answer was to high I would lower the percent for the 10% and if it was too low I would raise the percent for the 10%

Yeah you're supposed to solve it algebraically, not just trial and error.
I've done problems like this but I don't quite remember how

SlayerZ99 · October 10, 2011, 06:15:56 PM

So I think Im supposed to make 2 lines and put the point where they cross and such, but I have no clue what equations to put into the Y= screen. :C

SlayerZ99 · October 10, 2011, 06:25:17 PM

bump

IkeTheGeneric · October 10, 2011, 06:25:46 PM

op you're doing it right what do you have issues with lol

Headcrab Zombie · October 10, 2011, 06:30:44 PM

Yeah I'm not sure how you're supposed to solve it with two intersecting lines, but here's what I did and got the same answer as you. It's basically what you did except not trial and error guessing

2(x) + 10(100-x) = 8(100)

2, 10, and 8 are the strengths of the solutions (Using whole numbers is the same as using 0.02, 0.1, 0.08, you're just multiplying both sides by 100 which still keeps the equation true, I just find whole numbers easier to work with)
100 is the final desired amount of mixed solution

From here just solve for x, that's the amount of 2% solution, and then 100-x is the amount of 10% solution

Quote from: IkeTheGeneric on October 10, 2011, 06:25:46 PM

op you're doing it right what do you have issues with lol

He found it through trial and error and random guesses, sure he found the right answer but that's not exactly doing it right.

RedGajin · October 10, 2011, 06:31:30 PM

Answer: She has to drink the second bottle first, then the other one.

SlayerZ99 · October 10, 2011, 08:34:16 PM

So in my Y = screen I got the answer to this problem by doing this
Problem : Bicycle shop owner has bicycles and tricycles. He has 472 of them and there are a total of 1,095 wheels. How many of each type did the owner have
I put in

Y = 472 - X
Y = -1.5X + 547.5

and got 151 tricycles and 321 bicycles