First slide
Permutations
Question

If all the permutations of the letters in the word OBJECT are arranged (and numbered serially) in alphabetical order as in a dictionary, then the 717th word is

Moderate
Solution

The order of letters of the word 'OBJECT' is B C E J O T
Words starting with B can be formed in 5 ! ways.
Words starting with C can be formed in 5 ! ways.
Words starting with E can be formed in 5 ! ways.
Words starting with J can be formed in 5 ! ways.
Words starting with O can be formed in 5 ! ways.
Words starting with TB can be formed in 4! ways.
Words starting with TC can be formed in 4! ways.
Words starting with TE can be formed in 4! ways.
Words starting with TJ can be formed in 4! ways.
Words starting with TOB can be formed in 3 ! ways.
Words starting with TOC can be formed in 3 ! ways.
Words starting with TOE can be formed in 3 ! ways.
Words starting with TOJB can be formed in 2! ways.
Words starting with TOJC can be formed in 2! ways.
Therefore, the total number of words is 718 words.
Hence, 717th word is TOJCBE. 

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