The number of prime numbers lying between 393 and 401, both included, is:

Correct option is B

Given:

Find the number of prime numbers between 393 and 401 (both included).

Solution:

Check each number:

393 → divisible by 3 → not prime

394 → even → not prime

395 → ends with 5 → not prime

396 → even → not prime

397 → check divisibility by primes ≤ 20 → not divisible → prime

398 → even → not prime

399 → 3 + 9 + 9 = 21 → divisible by 3 → not prime

400 → even → not prime

401 → not divisible by primes ≤ 20 → prime

Prime numbers found: 397, 401

Total = 2 primes