How many prime numbers lie between 0 and 50 (count all primes p with 2 ≤ p ≤ 49)?

Difficulty: Easy

Correct Answer: 15

Explanation:


Introduction / Context:
Counting primes in a small interval checks quick recall of basic primes and composite recognition. The range 0 to 50 is common in aptitude tests and can be handled by enumeration or a mental sieve of Eratosthenes.


Given Data / Assumptions:

  • We count primes with 2 ≤ p ≤ 49 (since “between 0 and 50” excludes 50).
  • 1 is not prime.
  • Eliminate multiples of 2, 3, 5, and 7 as composites where applicable.


Concept / Approach:
List all primes under 50 and count them carefully, ensuring none are missed or misclassified.


Step-by-Step Solution:

Primes ≤ 49: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47.Count terms: there are 15 primes.Confirm that 49 (7 * 7) and 45, 35, etc., are composite and excluded.


Verification / Alternative check:
Mental sieve: strike out even numbers > 2, multiples of 3, of 5, and of 7; the remaining list matches the primes above.


Why Other Options Are Wrong:
13, 14, and 16 miscount by omitting or including numbers incorrectly; 12 is the count under 40, not under 50.


Common Pitfalls:
Including 1 as prime or forgetting 41, 43, and 47.


Final Answer:
15

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