# Thread: Help solving a algebraic system!

1. ## Help solving a algebraic system!

I need to finish 3 or 4 problems like this tonight,

0.4x + 0.1y = 0.28

x+y=25

also

"Medication A is given every 4 hours and Medication B is given twice each day. The total intake of the 2 meds is restricted to 50.6mg per day for a patient. If the ratio of the dosage of A to B is 5 to 8, find the dosage for each administration for each medication."

so I know the one equation is
6x+2y=50.6

I don't know how to do the other one...

thanks!

2. You can solve the first system of equations by substitution or by manipulating the equations and adding them.

If you multiply both sides of the first equation by -10, you get -4x - y = -2.8. Adding this to the second equation gives you -3x = 22.2, and you can solve the system from there.

For the second system, if the ratio of A to B is 5 to 8, then (according to your setup) x/y = 5/8, or x = 5y/8. You can substitute this value for x into the first equation in order to solve for y and then solve the system.

3. Well for the first problem I get the answer x=-7.4 and y=32.4

but it isn't really possible for x to be negattive according to the word problem since it's supposed to be a measurement of a solution

4. Originally Posted by emximer
Well for the first problem I get the answer x=-7.4 and y=32.4

but it isn't really possible for x to be negattive according to the word problem since it's supposed to be a measurement of a solution
Did you set up the equations yourself? It's possible you made an error there.

5. Well I went based on what another person told me to set up which was the same as how I had it set up, but you yourself gave me an x value of -7.4

"gives you -3x = 22.2" (from your earlier post)

So I guess the answer is negative? Perhaps I should email my prof.

EDIT: Heres the original problem so you can look and see if I set up the equations right

"A biologist has a 40% solution and a 10% solution, how many cubic centimeters of each should be mixed to obtain a 25cc of a 28% solution?"

6. Your first equation should be .4x + .1y = .28(25).

7. Originally Posted by icemanfan
Your first equation should be .4x + .1y = .28(25).
ahh thank you so much!

I get it now, x=15, y=10

many thanks!

so for my 2nd problem, I should do 2x+6y=50.6(5/8) ?

8. Originally Posted by emximer
so for my 2nd problem, I should do 2x+6y=50.6(5/8) ?
No. The total amount of the dosages is equal to 50.6. The ratio relates the dosages of the two medications (x and y), but the total taken should still be 50.6.