Ratio and Proportion
Since 2/5 of those lit at the beginning of an hour burn out during that hour, there are only 1 - 2/5 = 3/5 still burning at the end of the hour. therefore, after one hour 3/5 of the original number are still burning. After the second hour only 3/5 of those lit at the beginning of the second hour are still lit, but the number lit at the beginning of the second hour was 3/5 of the original number. So at the end of the second hour 3/5 of 3/5 = 9/25 of the original number are still lit. 9/25 is greater than 1/3 so continue. At the end of the
third hour 3/5 of 9/25 of the original number will be still lit. Since 3/5 of 9/25 is 27/125, which is less than 1/3, the correct answer is the third hour.
Related MCQ Ratio and Proportion
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