If a permutation is chosen at random from the letters "AAABBBCC", what is the probability that it begins with at least 2 A's?Round your answer to 6 decimal places as needed.
Question
If a permutation is chosen at random from the letters "AAABBBCC", what is the probability that it begins with at least 2 A's?Round your answer to 6 decimal places as needed.
Solution
To solve this problem, we need to calculate the total number of permutations of the letters "AAABBBCC" and the number of permutations that begin with at least 2 A's.
Step 1: Calculate the total number of permutations The total number of permutations of the letters "AAABBBCC" can be calculated using the formula for permutations of multiset: n! / (n1! * n2! * ... * nk!), where n is the total number of items, and n1, n2, ..., nk are the numbers of each type of item.
In this case, n = 8 (the total number of letters), n1 = 3 (the number of A's), n2 = 3 (the number of B's), and n3 = 2 (the number of C's).
So, the total number of permutations = 8! / (3! * 3! * 2!) = 560.
Step 2: Calculate the number of permutations that begin with at least 2 A's If a permutation begins with at least 2 A's, then we can think of the first two letters as being fixed as A's. This leaves us with 6 letters to permute, which are "ABBBCC".
The number of permutations of these 6 letters = 6! / (1! * 3! * 2!) = 60.
However, we also need to consider the case where the permutation begins with 3 A's. In this case, we have 5 letters to permute, which are "BBBCC".
The number of permutations of these 5 letters = 5! / (3! * 2!) = 10.
So, the total number of permutations that begin with at least 2 A's = 60 + 10 = 70.
Step 3: Calculate the probability The probability that a permutation chosen at random begins with at least 2 A's = the number of favorable outcomes / the total number of outcomes = 70 / 560 = 0.125.
Rounded to 6 decimal places, the probability is 0.125000.
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