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Ex 7.3,6 - Find n if  n-1P3 : nP4 = 1 : 9 - Chapter 7 - Permutation formula

Ex 7.3,6 - Chapter 7 Class 11 Permutations and Combinations - Part 2

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Ex 7.3, 6 Find n if n – 1P3 : nP4 = 1 : 9. Lets first calculate n – 1P3 and nP4 separately n – 1P3 = ((𝑛−1)!)/(𝑛−1 −3)! = ((𝑛−1)!)/(𝑛−4)! = (𝑛 − 1)(𝑛 − 2)(𝑛 − 3)(𝑛 − 4)!/(𝑛−4)! = (n – 1)(n – 2)(n – 3) It is given that n – 1P3 : nP4 = 1 : 9 "n – 1P3" /"n P4" = "1" /" 9" 9 (n – 1P3) = nP4 9(n – 1)(n – 2)(n – 3) = n(n – 1)(n – 2)(n – 3) 9"(n – 1)(n – 2)(n – 3)" /"(n – 1)(n – 2)(n – 3)" = n 9 = n n = 9

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Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 12 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.