Misc 4 - Chapter 7 Class 11 Permutations and Combinations

Transcript

Misc, 4 If the different permutations of all the letter of the word EXAMINATION are listed as in a dictionary, how many words are there in this list before the first word starting with E? In dictionary, words are given alphabetically We need to find words starting before E i.e. starting with A,B,C or D In EXAMINATION, there is no B,C or D,hence words should start with A Words in the list before the word starting with E = Words starting with letter A EXAMINATION Words starting with letter A Since letter are repeating, Hence we use this formula = !/ 1! 2! 3! Remaining letters = n = 10 Since, 2I, 2N p1 = 2, p2 = 2 Number of words formed by there letters = !/ 1! 2! = 10!/2!2! = 907200 Words in the list before the word starting with E = Words starting with letter A = 907200