How much does it cost to operate a 25-w soldering iron for 8.0 hours if energy costs 8.0¢/kwh?

1 answer:

6 0

The power P is defined as the energy E per unit of time t:
$P= \frac{E}{t}$
In our problem, the power is P=25 W and the total time is t=8.0h, so we can calculate the total energy used during this time:
$E=Pt=(25 W)(8.0 h)=200 Wh=0.2 kWh$
The energy costs 8€ per each kwh, so we can write the following proportion:
$8€: 1kwh = x:0.2 kWh$
where x is the price corresponding to 0.2 kWh. Solving the proportion we find x:
$x= \frac{(8€)(0.2 kWh)}{1kWh}=1.6$ €

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