UPSC NDA Math Model Paper 7

Here, we have to form a 5 letter code using first 6 letters of english alphabet such that no letter is letter repeated.
No. of ways to choose 1‌st letter for the code = 6
No. of ways to choose 2‌nd letter for the code = 5
No. of ways to choose 3‌rd letter for the code = 4
No. of ways to choose 4‌th letter for the code = 3
No. of ways to choose 5‌th letter for the code = 2
∴ The no. of ways to form a 5 letter code using first 6 letters of english alphabet = 6 × 5 × 4 × 3 × 2 = 720.