What is M = {x : x ∈ N, x is a two-digit prime number and x < 20}?
Answer and explanation
Correct answer: M = {11, 13, 17, 19}
The governing concept is filtering a set by all stated conditions. Two-digit natural numbers below 20 are 10 through 19. Among these, 11, 13, 17 and 19 have exactly two positive factors, so they are prime. Number 10 is composite, 12 is composite, and 2, 3, 5 and 7 are only one-digit primes. Therefore option A gives exactly M.
Frequently asked questions
What is the correct answer to this question?
M = {11, 13, 17, 19}
Why is this the correct answer?
The governing concept is filtering a set by all stated conditions. Two-digit natural numbers below 20 are 10 through 19. Among these, 11, 13, 17 and 19 have exactly two positive factors, so they are prime. Number 10 is composite, 12 is composite, and 2, 3, 5 and 7 are only one-digit primes. Therefore option A gives exactly M.
Which subject and chapter does this question cover?
This is a Class 9 Mathematics question. Chapter: Number Systems. Topic: General chapter practice.
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