If F₁ = {x : x ∈ ℕ, x has exactly two distinct positive factors and x < 15}, what is F₁?
Answer and explanation
Correct answer: F₁ = {2, 3, 5, 7, 11, 13}
A natural number has exactly two distinct positive factors precisely when it is prime: the number itself and 1. The prime numbers less than 15 are 2, 3, 5, 7, 11, and 13. The number 1 is not prime because it has only one positive factor, namely 1. Hence the required set is option B.
Frequently asked questions
What is the correct answer to this question?
F₁ = {2, 3, 5, 7, 11, 13}
Why is this the correct answer?
A natural number has exactly two distinct positive factors precisely when it is prime: the number itself and 1. The prime numbers less than 15 are 2, 3, 5, 7, 11, and 13. The number 1 is not prime because it has only one positive factor, namely 1. Hence the required set is option B.
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Sets. Topic: Sets and their representations.