Question 424941
During one month, a homeowner used 500 units of electricity and 100 units of gas for a total utility bill of $88. The next month, 400 units of electricity and 150 units of gas were used for a total bill of $76. What is the unit cost of both types of energy? 
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Equations:
500e + 100g = 88
400e + 150g = 76
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Multiply thru the 1st equation by (3/2) to get
750e + 150g = 132
400e + 150g = 76
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Subtract and solve for "e":
350e = 56
e = $0.16 or 16 cents per unit for electricity
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Solve for "g":
500e + 100g = 88
500*0.16 + 100g = 88
80 + 100g = 88
100g = 8
g = $0.08 or 8 cents per unit for gas
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Cheers,
Stan H.
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