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GATE 2025 CE (CE2) – Question 3

General Aptitude · Quantitative Aptitude: Arithmetic and Number Computation · 1 mark · Multiple choice

An electricity utility company charges ₹ 7 per kWh (kilo watt-hour). If a 40-watt desk light is left on for 10 hours each night for 180 days, what would be the cost of energy consumption? If the desk light is on for 2 more hours each night for the 180 days, what would be the percentage-increase in the cost of energy consumption?

  1. ₹ 604.8; 10%
  2. ₹ 504; 20%
  3. ₹ 604.8; 12%
  4. ₹ 720; 15%

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Correct answer: (B) ₹ 504; 20%

Explanation

The energy used is $0.04 \text{ kW} \times 10 \text{ h} \times 180 = 72$ kWh, which costs $72 \times 7 = ₹504$. With 2 more hours each night the energy is proportional to $12/10$, so the cost goes up by 20%.