2024 · Q30
If 11x + 5y is a prime number where x, y are natural numbers then what is the minimum value of (x + y)?
Elementary MathematicsNumber System
- A3
- B4
- C5
- D6
Explanation
Trying x+y = 2: 11+5 = 16 (not prime); x+y = 3: 21, 27 (not prime); x+y = 4: 26, 32, 38 (not prime). At x+y = 5, x=1, y=4 gives 11+20 = 31, which is prime. No smaller sum works, so the minimum x+y is 5 — option C.