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The power rating of electrical appliances can be used to calculate the cost of using them.

The following equation enables the number of units used to be calculated:

Number of units used = power rating in kW x time in hours

When using this equation it is important to remember that the power must be in kW and the time in hours.

Example

Calculate the cost of using a 2 kW heater for 6 hours if the price of a unit is 13p.

Number of units used = power rating in kW x time in hours

Time = 6 hours

Power rating = 2 kW

Number of units used = 2 kWh x 6 h = 12 kWh

total cost = number of units used × cost per unit

= 12 kWh x 13p

= 156p

= £1.56

The cost of using the heater is £1 .56