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Given
    • Ten different letters of an alphabet are given.
    • Out of the given letters, words with 4 letters are to be formed.

To find
    • The number of words that have at least one letter repeated.

Approach and Working out
Ways to form words having at least 1 letter repeated = Total number of words that can be formed – words with no letter repeated.
    • = 10 × 10 × 10 × 10 – 10 × 9 × 8 ×7
    • = 10,000 – 5040 = 4960

Hence, option E is the correct answer.

Correct Answer: Option E
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Solution:

The total number of 4-letter words that can be formed is 10 x 10 x 10 x 10 = 10,000. The total number of 4-letter words without any repeating letters that can be formed is 10 x 9 x 8 x 7 = 5,040. Therefore, the total number of 4-letter words (with at least one repeating letter) that can be formed is 10,000 - 5,040 = 4,960.

Answer: E
Thanks Scott.
In the last step, I calculated the units digit to arrive at option E.
\(n=10^4-10*9*8*7=10(10^3-9*8*7)\)
Units digit of \(9*8*7=4\)
Now, __0-__4=__6
Hence E.
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