Probability

Video Lecture 1 Khan Academy      - Permutation formula Combination formula Additional Rule Of Probability  

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Factorial and Prime

Factorial is defined only for natural numbers( no fractions and no negative numbers). 0! = 1 Unit digit of factorial of any number greater than 5 is always 0.  Exponent of a in in n!( Highest power of a in n!). a is a prime number. 11:54 Number of 0 in n!  24:00