Question

What is the elimination of 20x+5y=120 and 10x+7.5=80

Answer 1

20x+5y=120
10x+7.5y=80    multiply this one by 2
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20x+5y=120
20x+15y=160   subtract 

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        -10y=-40    divide both sides by -10 
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             y=4         

20x+5(4)=120   plug 4 in for y in the first equation 
20x+20=120     multiply 
20x=100           subtract 
x=5                   divide to find x