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AR15.COM
1/24/2013 1:55:45 PM EDT
I have a basic algebra problem as part of my physics online homework as a review and I nor my gf can not figure out it.  Either that or the online program is not taking our answers.  I have not done algebra since 06 so help is greatly appreciated.

Must solve for x and y

x +  y= 9.0

0.50 x+ 0.20y = 3.45

If you answer it would you mind please posting the steps?  I know you have to solve for one in the first step leaving
x = 9.0 - y

Its the 2nd half I am not sure about.

Thanks in advance,
Payton
1/24/2013 1:58:51 PM EDT
[#1]
Substitute one variable from EQ1 in EQ2
 
1/24/2013 2:02:02 PM EDT
[#2]
Quoted:
Substitute one variable from EQ1 in EQ2  



Yeah I knew that I just keep getting a wrong answer.
1/24/2013 2:02:10 PM EDT
[#3]
Replace the x in the second equation with (9 - y) and work it out.
1/24/2013 2:02:11 PM EDT
[#4]
fuck it, im too tired to do math, forget everything I said

EDIT: Ok here we go, ill try not to fuck it up this time:

x+y = 9

x+y-y = 9-y

x = 9-y

.5(9-y) + .2y = 3.45

4.5 - .5y + .2y = 3.45

4.5 - .5y + .2y - 4.5 = 3.45 - 4.5

-.3y = -1.05

-.3y / -.3 = -1.05/-.03 = y = 3.5

Wow, took me long enough eh? Someone should revoke my degree.

1/24/2013 2:02:35 PM EDT
[#5]







Quoted:




I have a basic algebra problem as part of my physics online homework as a review and I nor my gf can not figure out it.  Either that or the online program is not taking our answers.  I have not done algebra since 06 so help is greatly appreciated.
Must solve for x and y
x +  y= 9.0
0.50 x+ 0.20y = 3.45
If you answer it would you mind please posting the steps?  I know you have to solve for one in the first step leaving



x = 9.0 - y
Its the 2nd half I am not sure about.
Thanks in advance,



Payton




0.20y = 2.95



y = 2.95/.2 = 14.75



x = 9 - 14.75 = -5.75






ETA: I missed the 'x' in the 0.50x, which makes the above useless.





See the post above mine
 
1/24/2013 2:02:44 PM EDT
[#6]
^

If you know x = 9.0 - y, then you can substitute (9.0 - y) as x in the second equation to solve for y.  Then once you have y, solve for x in the top equation.

1/24/2013 2:03:39 PM EDT
[#7]

Given:
x+y = 9
.5x + .2y = 3.45




Therefore:

x = 9 - y




Therefore:

.5(9 - y) + .2y = 3.45






1/24/2013 2:03:41 PM EDT
[#8]
x+y = 9
0.5x + 0.2y = 3.45

x = 9-y

0.5(9-y) + 0.2y = 3.45
4.5 - 0.5y + 0.2y = 3.45
1.05 = 0.3y
y = 3.5

x=9-y
x = 9-3.5
x = 5.5

Now check your work by substituting your values for x and y into both original equations:

x + y = 9
5.5 + 3.5 = 9 OK

0.5x + 0.2y = 3.45
0.5 (5.5) + 0.2 (3.5) = 3.45
2.75 + 0.7 = 3.45 OK

1/24/2013 2:07:31 PM EDT
[#9]



Quoted:



Quoted:

Substitute one variable from EQ1 in EQ2  






Yeah I knew that I just keep getting a wrong answer.


try again it works.

 

Click To View Spoiler





1/24/2013 2:12:38 PM EDT
[#10]
Next step is substitute x in Eq2 for its value in EQ1

So it looks like

0.50  (9.0 - y) + 0.20y = 3.45

4.5 - .5y + .2y=3.45

- .5y + .2y= -1.05

-.3y=-1.05

y=3.5

then solve for x in the first EQ
1/24/2013 2:18:09 PM EDT
[#11]
Write as matrix

Av=b
[1 1; 0.5 0.2] [ x; y ]=[ 9; 3.45 ]

Row reduce A\\b

x = 5.5, y = 3.5

Write exactly that, your professor will mark it right.
1/24/2013 2:26:52 PM EDT
[#12]
If you don't know that, you really shouldn't be taking physics I have to do all sort of multivariable calculus for my physics
1/24/2013 2:31:14 PM EDT
[#13]
288
1/24/2013 3:04:00 PM EDT
[#14]
Quoted:

Quoted:
Quoted:
Substitute one variable from EQ1 in EQ2  



Yeah I knew that I just keep getting a wrong answer.

try again it works.  
Click To View Spoiler




He probably forgot to distribute the decimal to the constant and the variable in the second equation.
1/24/2013 3:23:02 PM EDT
[#15]
Solve for x, y and z.

x + y = 87

0.87x + 0.87y + 0.87z = 3.14