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

Solution:

When repetition of alphabets is not allowed:
No. of ways of choosing first alphabet = 10
No. of ways of choosing second alphabet = 9
No. of ways of choosing to third alphabet = 8
No. of ways of choosing to fourth alphabet = 7
By fundamental counting principle,
Total possible number of ways = 10×9×8×7= 5040

NCERT Solutions Class 11 Maths Chapter 7 Exercise 7.1 Question 3

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

Summary:

The total number of 4-letter codes can be formed using the first 10 letters of the English alphabet, if no letter can be repeated is 5040