analysis of success of candidate attempt wise

From the 65th annual report of UPSC, we find following data about the success rate of aspirants in civil services exam:

15%	Of the toppers have cleared in their first attempt.
26%	In second attempt
26%	In third attempt. So cumulatively 67% OR 2/3rd of the toppers have cleared within first three attempts.
18%	In fourth attempt. So, cumulatively 85% of the toppers have cleared within first four attempts.
15%	In fifth or above attempt.