Question

During one month, a homeowner used 500 units of electricity and 100 units of gas for a total cost of $333. The next month, 400 units of electricity and 150 units of gas were used for a total cost of $286. Find the cost per unit of gas.

Answer 1

Answer: the cost per unit of gas is $0.28

Step-by-step explanation:

Let x represent the cost per unit of electricity.

Let y represent the cost per unit of gas.

During one month, a homeowner used 500 units of electricity and 100 units of gas for a total cost of $333. This is expressed as

500x + 100y = 333 - - - -- - -- - -- -1

The next month, 400 units of electricity and 150 units of gas were used for a total cost of $286. This is expressed as

400x + 150y = 286 - - - - - - - - - --2

Multiplying equation 1 by 400 and equation 2 by 500, it becomes

200000x + 40000y = 133200

200000x + 75000y = 143000

Subtracting, it becomes

- 35000y = - 9800

y = - 9800/- 35000

y = 0.28

Substituting y = 0.28 into equation 2, it becomes

400x + 150 × 0.28 = 286

400x = 286 - 42 = 244

x = 244/400 = 0.61