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NSW HSC · Mathematics Standard 2

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Q16 · Rates and Ratios3 marks

A 1.8 kW heater is used for 4 hours 30 minutes each day for 14 days. Electricity costs 33.4 cents per kWh. Calculate the cost of running the heater, in dollars.

  1. 4 h 30 min = 4.5 h✓ 1
  2. Time in hours before you multiply
  3. Energy = 1.8 × 4.5 × 14 = 113.4 kWh✓ 1
  4. Power × hours × days
  5. Cost = 113.4 × 33.4 = $3787.560 / 1
  6. Marker: 33.4 cents is $0.334 per kWh, so the cost is $37.88.
2 / 3Mark to win back: cents read as dollars

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