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During one month, a homeowner used 200 units of electricity and 140 units of gas for a total cost of $86.60. The next month, 210 units of electricity and 200 units of gas were used for a total cost of $101.00. Find the cost per unit of gas.

Answer 1

There are two unknowns, e (cost per unit of electricity) and g (cost per unit of gas).  So we need two equations.

 

200e + 140g = 86.60

210e + 200g = 101.00

 

200e = 86.60 - 140g

e = 0.433 - 0.7g

 

210(0.433 - 0.7g) + 200g = 101.00

90.93 - 147g + 200g = 101.00

53g = 10.07

g = 0.19

 

So gas is 19 cents per unit.