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Previous Year Question (PYQs)



If three letters can be posted to any one of the $5$ different addresses, then the probability that the three letters are posted to exactly two addresses is:





Solution

Total ways = each letter can go to any of 5 addresses 
$ = 5^3 = 125 $

Favourable cases (exactly two addresses used): 

Step 1: Choose 2 addresses out of 5 $ = \binom{5}{2} = 10 $

Step 2: Distribute 3 letters among these 2 addresses such that both are used Total ways to assign = $ 2^3 = 8 $

Subtract cases where all letters go to one address $ = 2 $

So valid distributions $ = 8 - 2 = 6 $

Total favourable $ = 10 \times 6 = 60 $

Probability $ = \frac{60}{125} = \frac{12}{25} $

Final Answer: $ \boxed{\frac{12}{25}} $



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