Is in Necessary to take Coaching For IITJEE Preparation ?

Why is it necessary to take accurate measurements ?

If the letters of the word IITJEE are permuted in all possible ways and the strings thus are arranged in the dictionary order find the rank of the word IITJEE.

If the letters of the word IITJEE are permuted in all possible ways and the strings thus formed are arranged in the lexicographic order, find the rank of the word IITJEE.

This is necessary for the preparation of slide ......

Is the presence of oxygen necessary during the preparation of bleaching powder ?