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JEE Advanced 2017 Mathematics question

MathematicsPermutations and CombinationsJEE Advanced 2017

Words of length 10 are formed using the letters A, B, C, D, E, F, G, H, I, J. Let be the number of such words where no letter is repeated; and let be the number of such words where exactly one letter is repeated twice and no other letter is repeated. Then,

Answer: 5

Solution

. For : choose the repeated letter (10 ways) and 8 other distinct letters from the remaining 9 ( ways); arrange the 10 letters

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Question ID VK-026638