Answer:
X = 14 kg
Y= 7 kg
Step-by-step explanation:
LET Â X and Y equal the amounts of brand X and Y
X = kg of brand X
Y = kg of brand Y
we know:
1) Â X Â Â + Â Â Y Â = Â 21 Â Â (kg)
2) Â 1X Â + Â 4Y Â = Â 2(X + Y) Â Â Â Â (This is the cost/kg * amounts for total cost) Â
Coefficients 1,4,2 Â are the cost/kg)
substitute eq. 1 (X+Y), = 21 into right side of equation 2
1X + 4Y = (21)*2
use elimination to solve 2 equations
X Â + Â Y = 21
X Â + 4Y = 42 Â Â Â Â (now subtract, Â Â Â note: Â I wrote the 1X as just X)
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0   -3Y  = -21    OR  Y = 7 kg  so X = (21-7) OR  X = 14 kg