Question 186715
my teacher says we need the bottom equation to solve the top equation then to find the answer to the bottom equation after.
0.3x-0.2y = 0.5  (top equation)
   x-  2y = -5   (bottom equation)
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Taking the "bottom equation", let's solve for 'x':
   x-  2y = -5
adding 2y to both sides we get:
   x = 2y -5
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Now, we take the above, and substitute it into the "top equation":
0.3x-0.2y = 0.5
0.3(2y -5)-0.2y = 0.5
distributing the 0.3 to terms inside the parenthesis:
0.6y-1.5 -0.2y = 0.5
combining y's:
0.4y-1.5 = 0.5
adding 1.5 to both sides:
0.4y = 2
y = 2/0.4
y = 5  (solution for y)
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Finally, we take the above solution of y and plug it back into the bottom equation and solve for x:
   x-  2y = -5 
   x-  2(5) = -5 
   x-  10 = -5 
adding 10 to both sides:
   x = 5 (solution for x)
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Solution:
y=5
x=5
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The above method is called the "substitution method".