x = cups of the first mixture
y = cups of the second mixture
sugar equation:
salt equation:
Solve by elimination: multiply the first equation by 3 and subtract the second equation.
0.6x + 1.5y = 24
0.6x + 0.3y = 6
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1.2y = 18
y = 18/1.2 = 15
Substitute y=15 in one of the original equations:
ANSWER: 2.5 cups of the first mixture and 15 cups of the second.
CHECK:
sugar: 0.2(2.5)+0.5(15) = 0.5+7.5 = 8
salt: 0.6(2.5)+0.3(15) = 1.5+4.5 = 6