Q.3. How many 4-letter code can be formed using the first 10 letters of the English alphabet, if no letter can be repeated?
There are 10 letters of English alphabets.
As we know that repetition of the letters is not allowed,
so, the first place can be filled by any of 10 letters.
Second place can be filled with any of the remaining 9 letters.
Third place can be filled with any of the remaining 8 letters.
The fourth place can be filled with any of the remaining 7 letters.
Number of 4-letter code can be formed when the repetition of letters is not allowed
Hence, 5040 4-letter codes can be formed using the first 10 letters of the English alphabet, if no letter can be repeated.