InterviewSolution
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How many different words can be formed from the letters of the word ‘GANESHPURI’? In how many of these words:(i) the letter G always occupies the first place?(ii) the letter P and I respectively occupy the first and last place?(iii) Are the vowels always together?(iv) the vowels always occupy even places? |
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Answer» Given as The word ‘GANESHPURI’ Here 10 letters in the word ‘GANESHPURI’. Total number of words formed is 10P10 = 10! (i) the letter G always occupies the first place? If we fix the first position with letter G, now remaining number of letters is 9. Number of arrangements of 9 things, taken all at a time is 9P9 = 9! Ways. Thus, a possible number of words using letters of ‘GANESHPURI’ starting with ‘G’ is 9! (ii) the letter P and I respectively occupy the first and last place? If we fix the first position with letter P and I in the end, now remaining number of letters is 8. Number of arrangements of 8 things, taken all at a time is 8P8 = 8! Ways. Thus, a possible number of words using letters of ‘GANESHPURI’ starting with ‘P’ and ending with ‘I’ is 8! (iii) Are the vowels always together? Here 4 vowels and 6 consonants in the word ‘GANESHPURI’. Considering 4 (A,E,I,U) vowels as one letter, now total number of letters is 7 (A,E,I,U, G, N, S, H , P, R) Number of arrangements of 7 things, taken all at a time is 7P7 = 7! Ways. (A, E, I, U) can be put together in 4! Ways. Thus, total number of arrangements in which vowels come together is 7! × 4! (iv) the vowels always occupy even places? The number of vowels in the word ‘GANESHPURI’ = 4(A, E, I, U) The number of consonants = 6(G, N, S, H, R, I) The even positions are 2, 4, 6, 8 or 10 Then, we have to arrange 10 letters in a row such that vowels occupy even places. Here 5 even places (2, 4, 6, 8 or 10). 4 vowels can be arranged in these 5 even places in 5P4 ways. The remaining 5 odd places (1, 3, 5, 7, 9) are to be occupied by the 6 consonants in 6P5 ways. Therefore, by using the formula, P (n, r) = n!/(n – r)! P (5, 4) × P (6, 5) = 5!/(5 – 4)! × 6!/(6 – 5)! = 5! × 6! Thus, number of arrangements therefore that the vowels occupy only even positions is 5! × 6! |
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