Question

Which one of the following is an odd composite number?
(a) 7
(b) 9
(c) 11
(d) 12

Answer 1

Hint: First of all try to recollect what odd numbers are and what composite numbers are. Now check each option if they satisfy the conditions for both odd and composite numbers and pick out the correct answer.

Complete step by step answer:
Before proceeding with the question, let us see what odd and composite numbers are:
Odd numbers: Any integer that cannot be completely divided by 2 or we can say that integer that gives remainder as 1 when we divide it by 2 is called an odd number. Examples are 1, 3, 35, – 47, etc.
Composite numbers: Whole numbers that have more than two factors or we can say that numbers that have factors other than 1 and itself are called composite numbers. Examples are 4, 9, 15, 28, etc.
Now, let us consider our question and check which option satisfies the condition for both the odd and composite number.
(a) 7
When we divide 7 by 2, it gives the remainder as 1. So, 7 is an odd number. The factors of 7 are just 7 and 1. So, this is not a composite number. Hence 7 is not our answer.
(b) 9
When we divide 9 by 2, it gives the remainder as 1. So, 9 is an odd number. The factors of 9 are 1, 3 and 9. So, this is a composite number. Therefore, 9 is an odd composite number. Hence 9 is our answer.
(c) 11
When we divide 11 by 2, it gives the remainder as 1. So, 11 is an odd number. The factors of 11 are just 11 and 1. So, this is not a composite number. Hence 11 is not our answer.
(d) 12
When we divide 12 by 2, it gives the remainder as 0. So, 12 is not an odd number. The factors of 12 are 1, 2, 3, 4, 6 and 12. So, this is a composite number. Hence 12 is not our answer.

So, the correct answer is “Option b”.

Note: In this question, students must select only those options which satisfy the conditions for both odd and composite and not just one. Also, some students think that all odd numbers are not composite or prime which is wrong because the numbers like 9, 15, etc. are odd and composite. Similarly, we can’t say that all even numbers are composite as 2 is an even prime number though we can say that all positive even numbers except 2 are composite numbers.