SOLUTION: Solve each system of equations by using substitution. {{{ 8x + 9y = 9 }}} {{{ 3x - 5y = 20 }}} I've multiplied the bottom equation by 3 and got 9x - 15y = 60, but it i

Algebra ->  Systems-of-equations -> SOLUTION: Solve each system of equations by using substitution. {{{ 8x + 9y = 9 }}} {{{ 3x - 5y = 20 }}} I've multiplied the bottom equation by 3 and got 9x - 15y = 60, but it i      Log On


   

Question 477473: Solve each system of equations by using substitution.
+8x+%2B+9y+=+9+
+3x+-+5y+=+20+


I've multiplied the bottom equation by 3 and got 9x - 15y = 60, but it isn't going to be correct because 8x - 9x = -x so the x hasn't been eliminated. I don't know what to do about it. The rest of the problem made no sense because the numbers were too high after I plugged them in. I got -x + -6 = -51 then divided that by -6 which got me 8.5. I didn't know what to do with the -x so I just ignored it bu I don't think that's right. Any solutions?
Found 2 solutions by Alan3354, ewatrrr:
Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
Solve each system of equations by using substitution.
+8x+%2B+9y+=+9+
+3x+-+5y+=+20+
------------------------
You have to solve one of the eqns for x or y, then sub into the other eqn.
Substitution is not the best method for these 2, but sometimes you don't get to choose.
+3x+-+5y+=+20+
+x+=+%285y+%2B+20%29%2F3+
-------------
+8x+%2B+9y+=+9+
+8%285y%2B20%29%2F3+%2B+9y+=+9+
Multiply by 3 to eliminate fractions
+40y+%2B+160+%2B+27y+=+27+
67y = -133
y = -133/67
-------------
Sub for y in either eqn and find x
+x+=+%285y+%2B+20%29%2F3+
x = (-665/67 + 1340/67)/3
x = 225/67

Answer by ewatrrr(24785) About Me  (Show Source):
You can put this solution on YOUR website!
 

Hi,

Solve each system of equations by using substitution.

using Substitution

 8x + 9y = 9 OR   y = (-8/9)x + 1

 3x - 5[(-8/9)x + 1] = 20

 3x + 40/9x - 5 = 20

 27x + 40x - 45 = 180

        67x = 225

          x = 225/67  and y = (-8/9)225/67 + 1 = -1.9851

using Elimination 

 8x  +  9y = 9

27/5x - 9y = 36  |Recommend multiplying thru with 9/5 to eliminate y

    67/5x = 45

        x = 225/67 etc