SOLUTION: The problem is as follows- Solve by useing Substitution: x+y=20} 5x+10y=200} I made it so the equation read y=20-x so then i substituted that for the equatioin 5x+10y=200. It

Question 11390: The problem is as follows-
Solve by useing Substitution:
x+y=20}
5x+10y=200}
I made it so the equation read y=20-x
so then i substituted that for the equatioin 5x+10y=200. It eventualy came out to -5x=0. But just today my algebra2 teacher said that is a wrong outcome for any problem like this. Ive done it over and over but I'm still geting that answer. Can you please help me?
Answer by tishy(4) (Show Source): You can put this solution on YOUR website!
x+y=20.....equation 1
5x+10y=200....equation 2
multiply equation 1 by negative 5
therefore you get (x) x -5, y x-5 and 20 x -5 (you must multiply everything my negative 5)
so your new equation would be -5x-5y= -100
so you work with your new equation -5x-5y= -100
5x + 10y= 200
NOTICE I made my x into a a negative 5 so that it may cross out ot contradict with the 5 in equation 2. so when i work out my problem those two will be elimianted watch closely
-5x-5y = -100
5x +10y = 200
therefore when i work it out the negative 5 has cancelled my 5 in equa. 2 so i am left with
-5y = -100
+10y = 200 (so i work it ot from here on)
you ALWAYS ADD AFTER YOU HAVE DONE YOUR CANCELATION(the cancelling i did with teh 5's) so now
-5y + 10y = 5
ans -100 + 200 (o i FORGOT YOU MUST ALWAYS ADD THE 2 NUMBERS AT THE END OF THE EQUATION ALSO)
so i am left with 5 = 100 ( now what i do with this is divide) so my answer would be 100/5y = 20
so therefore in my 1st part i have discovered that y = 20
so now i have to subsitute to ensure that that is correct
with substituion you can use any equation i will choose to use equation 2
so
5x + 10y = 200 now becomes:
5x +10(x20) = 200 (because i substitued)
5x + 200 = 200 ( so what i do next is carry the 200 on the left over to the right becasue there is a rule that states ONLY VARIABLES which are the letters can remain on the left)
so now my problem looks like this
5x = 200 - 200 which works out to
5x = 0
HEY you did a Great job at trying to do it you only got mix up with your negative sign i hope this is right bye !!!!

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