UPSC NDA I 2021 Mathematics Solved Paper

Concept
Prime number: Prime number are those which are divisible by itself and 1 .
Calculation:
Not a single five-digit prime number can be formed using the digits 1,2,3,4,5 (without repetition). This is because if one adds the digits, the result obtained will be =1+2+3+4+5=15 which is divisible by 3
Hence, any number obtained as a permutation of these 5 digits will be at least divisible by 3 and cannot be a prime number.