GATE CE 2025 Set 2 — Question 3
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General Aptitude → Quantitative Aptitude → Ratios, Percentages, Powers, Exponents & Logarithms
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Question
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?
Correct answer
(B) ₹ 504; 20%
Solution
1.Calculate initial energy consumption ():
2.Calculate initial cost ():
3.Calculate percentage increase in cost:
The time increases from 10 hours to 12 hours (an increase of 2 hours). Since power, the rate per kWh, and the number of days remain constant, the percentage increase in cost is directly proportional to the percentage increase in time:Thus, the initial cost is ₹ 504 and the percentage increase is 20%, which corresponds to option (B).
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