How many 4-letter code can be formed using the first 10 letters of the English alphabet, if no letter can be repeated?

Explanation

No. of was of choosing first letter = 10
No. of ways of choosisng second letter = 9
No. of ways of choosing third letter = 8
No of ways of choosing fourth letter = 7
No. of required code words
`= 10 xx 9 xx 8 xx 7 = 5040`