It takes about four minutes to bake a potato in a 1000 W microwave oven. How much energy is used?

Energy used equals power multiplied by time. A 1000 W microwave uses 1 kW, and 4 minutes is 4/60 hours, so the energy is 1 × 4/60 ≈ 0.067 kWh. Rounded to two significant digits, that is 0.07 kWh, choice B.

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