Four different candles, which can last for 5 hours, 4 hours. 3 hours and 2 hours of burning, respectively, are lit in a room at the same instant and allowed to burn till such time that the three candles in the room get extinguished. The cost of burning ea

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Q: 57 (IAS/2003)
Four different candles, which can last for 5 hours, 4 hours. 3 hours and 2 hours of burning, respectively, are lit in a room at the same instant and allowed to burn till such time that the three candles in the room get extinguished. The cost of burning each one of these candles is 75 paise per hour. The cost involved is:

question_subject: 

Maths

question_exam: 

IAS

stats: 

0,4,1,0,1,4,0

keywords: 

{'different candles': [0, 0, 1, 0], 'candles': [0, 0, 1, 0], 'burning': [1, 0, 1, 2], 'cost': [2, 1, 2, 10], 'hours': [7, 2, 16, 9], 'hour': [5, 5, 11, 12], 'paise': [0, 0, 1, 1]}

The question is about the cost of burning three candles till they get completely extinguished. The candles have different lifespans: one can burn for 5 hours, another for 4 hours, the third for 3 hours, and the last for 2 hours. As per the setup, we are supposed to calculate the cost until three of the candles are extinguished. This means we treat the scenario only till the third longest burning candle extinguishes, which is after 3 hours.

Option 1 and 2, Rs. 2.75 and Rs. 3.75 respectively, are not feasible as even a single candle costs more to burn for 3 hours (75 paise x 3 hours = Rs. 2.25).

Option 4, Rs. 12.50, overestimates the duration of burning.

So, the correct answer is option 3, Rs. 9.75. This is because for these 3 hours, four candles are burning simultaneously, which makes the cost 4 (candles) x 75 paise (cost per hour) x 3 hours = Rs. 9.