Let p, q, r and s be positive natural numbers having three exact factors including 1 and the number itself. If q > p and both are two digit numbers, and r > s and both are one-digit numbers, then the value of the expression is:
Show answer & explanation
Correct answer: A
Explanation
The correct answer is option 1 i.e. -s-1
One can solve this by hit and trial,
Having only three-factor means the number must be a square of a prime number.
r > s and both are one - digit numbers,
The only possible value of r and s is 9 and 4.
If q > p and both are two-digit numbers, then the only possible value of p and q is 49 and 25
= (25 - 49 - 1)/(9 - 4)
= -25/5 = -5
-5 = -4 - 1
-5 = -s - 1.