The written exam is only for 1750 marks. Out of this 250 marks are assigned for essay. If we remove these marks, then, the written exam is for 1500 marks. Suppose you score 825 out of 1500, which is 55% and is considered to be a good score in IAS. You have scored these marks on studying the subject. Marks for essay are not included in this score.
The problem with the essay paper is that you can get from minimum 10% to 75% marks. 10% means 25 marks and 75% means 187.5 marks. Hence, the maximum round off marks is 185 and minimum are 25. This way the difference between minimum and maximum marks is 160. Let's imagine that you have scored 825 in rest of the exams. Now if you score 20% in essay, then, your total score wouldbe 825+50= 875. Hence, your percentage would be 50 since you have scored 875 out of 1750.
Now let's talk of a student who has scored 50% mark in other papers excluding essay. That means 750 out of 1500. He can score 75% in essay. But we suppose that he has scored 60%, which is not difficult. Now his total score is 750+ 150= 900.
Now let's calculate this score. Even after scoring 55% in 6 papers, the first student's total score was 875 since he could score only 20% in essay. On the other hand the second student got only 50% in 6 papers. But finally he scores more than the first student by 25 marks since he scores 60% in essay-irrespective of the fact that he was 75 marks behind in the re t of the papers as compared to the first student. It was only by scoring more in essay that he moved ahead of the first student. Just think that if the first student scores 50% rather than 20° 0 in essay, which is not very difficult, then, his total marks would be 950. 950 out of 1750 mean 54.8%. That means selection i definite, that too, with a good rank. My question is how was this difference created? Very clear answer- essay.