SOLUTION: In a string of length 9 with elements being a, b or c. How many strings will contain at least 6 b’s?

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Question 370132: In a string of length 9 with elements being a, b or c. How many strings will contain at least 6 b’s?
Answer by edjones(8007) About Me  (Show Source):
You can put this solution on YOUR website!
expand(b+a+c)^9
1 b^9
2*9 b^8...
2*36+72 b^7...
2*84+252*2 b^6...
-------add
835 strings will contain at least 9 b's.
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Ed