Question 345986
sry i dont have time to do all those questions but as for the #4
a) you should be able to do in your head using elimination method.
X + 2Y + Z = 22 
X + Y = 15 
3X + Y + Z = 37 
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X + 2Y + Z = 22 
-(X + Y = 15)
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Y + Z = 7
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3X + Y + Z = 37 
-(Y + Z = 7)
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3X=30
{{{highlight(X=10)}}}
X + Y = 15
{{{highlight(Y=5)}}}
Y + Z = 7
{{{highlight(Z=2)}}}
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<p>
b)start with the first two
 10X + Y + Z = 603
 8X + 2Y + Z = 603
 20X - 10Y - 2Z = -6
<p>
10X + Y + Z = 603
-(8X + 2Y + Z = 603)
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2X - Y = 0    
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2X - Y = 0   (multiply this whole thing by 10) 
20X - 10Y = 0    
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20X - 10Y - 2Z = -6
-(20X - 10Y = 0)
-2Z = -6
{{{highlight(Z=3)}}}
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