Question

The cost of energy delivered to residences by electrical transmission varies from $0.070/kWh to $0.258/kWh throughout the United States; $0.110/kWh is the average value. (a) At this average price, calculate the cost of leaving a 40-W porch light on for two weeks while you are on vacation? (b) At this average price, calculate the cost of making a piece of dark toast in 3.00 min with a 925-W toaster?

Answer 1

Answer:

(a)  $1.48

(b)  $0.0051 . . . . slightly more than 1/2¢

Step-by-step explanation:

  cost = (kW)(hours)(cost/kWh)

(a) cost = (0.040 kW)(24 h/da)(14 da/wk)($0.11/kWh) ≈ $1.478

The cost of leaving the porch light on is about $1.48.

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(b) cost = (0.925 kW)(3 min)/(60 min/h)($0.11/kWh) ≈ $0.00509

The cost of toasting bread is about 0.5 cents.