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February 27, 2015

February 27, 2015

Posted by **SAP** on Thursday, September 30, 2010 at 8:02pm.

7r-4s=-7

4r+7s=61

- Math need by 9pm cst -
**bobpursley**, Thursday, September 30, 2010 at 8:05pmmultiply the top equation by 7, and the bottome equation by 4.

Then add the equations, which will eliminate the s variable.

I will be happy to critique your work

- Math need by 9pm cst -
**SAP**, Thursday, September 30, 2010 at 9:11pm7r-4s=-7 (7)

4r+7s=61 (4)

49r - 28s = -49

16r + 28s = 244

---------------

65r = 195

195/65 = 3 (simplified) (3, is the first number of the ordered pair.)

Now this is the part that I get lost on. I know I am suppose to substitute 3 into one of the equations above, but how do I determine which one. So if I substitute 3 into the 1st equation:

7(3)-4s= -7

21 - 4s= -7

------------

21 = -7 would my answer be -7/21

Substitute 3 into the 2nd equation:

4(3)+7s = 61

12 + 7s = 61

-------------

12 = 61 would my answer be 61/12

(3, is the first number of the ordered pair.)

(3,-7/21) or (3,61/12) which ordered pair is correct?

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