Question 581222
probability:   p(x) = {{{f(x)/sum f(x)}}}

x(no. of attempts of CAT) | f(x)(no. of students  |    p(x) (probability)
             1            |      721,769          |  721,769/1518,859 = 0.4752 
             2            |     601,325           |  601,325/1518,859 = 0.3959
             3            |      166,763          |  166,763/1518,859 = 0.1098
             4            |      22,299           |  22,299/1518,859  = 0.0147
             5            |      6,730            |  6,730/1518,859   = 0.0044
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            sum           |      1518,859         |              1

find sum of all students. it is sum f(x) = 1518,859  
and sum of probabilitis should be 1 always.