Question 421771
no. of ways by an organisation can held convention =30


no. of ways for 4 organisation  = 30 * 30 *30 *30 = (30)^4


no. of ways when all have different days = 30 * 29 * 28 *27 = 657720


probability that all have different day convention  i.e P(A)= 657720/(30)^4


probability that at least two have same day convention i.e P'(A) 

= 1- P(A)

= 1 - 657720/(30)^4


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