Which number is prime between 10 and 20?

Which number is prime between 10 and 20?

• A. 11
• B. 10
• C. 12
• D. 14

Answer: (A)

Prime numbers are integers greater than 1 that have exactly two distinct positive divisors: 1 and the number itself. To check 11, note that its square root is about 3.3, so you only need to test divisibility by 2 and 3. It isn’t divisible by either, so 11 has only 1 and 11 as divisors and is prime. The other options are not prime because they are even and divisible by 2 (10, 12, and 14). Between 10 and 20, there are other primes as well, like 13, 17, and 19, but among the given numbers only 11 fits the definition.

Prime numbers are integers greater than 1 that have exactly two distinct positive divisors: 1 and the number itself. To check 11, note that its square root is about 3.3, so you only need to test divisibility by 2 and 3. It isn’t divisible by either, so 11 has only 1 and 11 as divisors and is prime. The other options are not prime because they are even and divisible by 2 (10, 12, and 14). Between 10 and 20, there are other primes as well, like 13, 17, and 19, but among the given numbers only 11 fits the definition.