PERMUTATION & COMBINATION 1. FUNDAMENTAL PRINCIPLE OF COUNTING (counting without actually counting): If an event can occur in 'm' different ways, following which another event can occur in 'n' different ways, then the total number of different ways of (a) Simultaneous occurrence of both events in a definite order is \(m\) \(× n\) . This can be extended to any number of events (known as multiplication principle). (b) Happening of exactly one of the events is \(m + n\) (known as addition principle). All Chapter Notes, Concept and Important Formula 2. FACTORIAL: A Useful Notation \(: n != n ( n -1)( n -2) \ldots \ldots\) . \(2.1\) ; \(n !=n .(n-1) !\) where \(n \in W\) \(0 !=1 !=1\) \((2 n) !=2^{n} \cdot n ![1.3 .5 .7 \ldots \ldots . .(2 n-1)]\) Note that : (i) Factorial of negative integers is not defined. (ii) Let \(p\) be a prime number and \(n\) be a positive integer, then exponent of \(p\) in \(n !\) is denoted by \(E _{ p }( n !)\) and is given by \(...
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