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

Algebra ->  Expressions-with-variables -> 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      Log On


   

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) About Me  (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 !!!!