If n is a positive integer and r is the remainder when (n-1)(n+1) is divided by 24. What is the value of r?
1. n is not divisible by 2
2. n is not divisible by 3
1. We know n is not divisible. So, n-1 & n+1 is definitely divisible by 2. But, it's not sufficient to determine 'r'.
2. Even this option does not lead anywhere.
If 'n' is not divisible by 2 & 3, it has to be a prime number or a product of prime numbers.
Now, take some examples of such numbers (5,7,35,95 etc.). And you will find that remainder is always '0'.
I am ready to fall, but not before I fly.