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Ex 7.3, 9 - How many words can be made from MONDAY - Class 11 - Permutation- repeating

  1. Chapter 7 Class 11 Permutations and Combinations
  2. Serial order wise
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Ex 7.3, 9 How many words, with or without meaning can be made from the letters of the word MONDAY, assuming that no letter is repeated, if 4 letters are used at a time, Total number of alphabets in MONDAY = 6 Hence n = 6 If 4 letters are used at a time, r = 4 Number of different words = nPr = 6P4 = (6! )/(6 −4)! = 6!/2! = (6 × 5 × 4 × 3 × 2!)/2! = 6 × 5 × 4 × 3 = 360 Ex7.3, 9 How many words, with or without meaning can be made from the letters of the word MONDAY, assuming that no letter is repeated, if (ii) all letters are used at a time, Total number of alphabets in MONDAY = 6 Hence n = 6 If all letters are used at a time, r = 6 Number of different words = nPr = 6P6 = (6! )/(6 − 6)! = 6!/0! = 6!/1 = 6! = 6 × 5 × 4 × 3 × 2 × 1 = 720 Ex 7.3, 9 How many words, with or without meaning can be made from the letters of the word MONDAY, assuming that no letter is repeated, if (iii) all letters are used but first letter is a vowel? First letter should be a vowel (a, e, i, o, u) Vowel in MONDAY are O and A If first letter is O, word will be of the form Number of letters left = 5 n = 5 Number of letters to be used = 5 r = 5 Number of different words = 5P5 = 5!/(5 − 5)! = 5!/0! = 5!/1 = 5! = 5 × 4 × 3 × 2 × 1 = 120 Similarly, If first letter is A , word will be of the form Number of letters left = 5 n = 5 Number of letters to be used = 5 r = 5 Number of different words = 5P5 = 120 Required number of words = 120 + 120 = 240

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