Question
Wed March 21, 2012 By:
I have seen that in many questions, in order to solve the given problem, sometimes normal P(event)/P(total) formula are used whereas somewhere 'nCr' has been made use of...
 

Doubt regarding choice of formula...

Expert Reply
Thu March 22, 2012
Both the techniques are correct , we can help u by giving an example ,
Lets say u have to calculate probability of an event where a dice is tossed thrice , number 6 appears only once .
 
The above problem can have sample spaces { 6 , not 6 , not 6 } , {not 6 , 6 , not 6} , {not 6 , not 6 , 6}
So probability =  3 * 1/6 * 5/6 * 5/6
But we can also say that out of the three probabilities 2 are same 5/6
So answer can be
1/6 * 5/6 * 5/6 * 3C2
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