Is 81 is a composite number or not ?
- As we already know that, the number having factors 1 and the number itself is the prime number.
- And numbers having more than these two factors are the composite numbers.
- To check whether the number 81 is composite or not first we have to find its factors.
Contents
Factors of 81:
- If we have taken numbers from 1, 2, 3…for checking factors of 81, we found that 81 has factors 1, 3, 9, 27 and 81. Hence, we must say that 81 is a composite number.
- Thus, 81 is the composite number.
- If we multiply 81 by 1, 2, 3 then we get the multiples of 81 which are 81, 162, and so on.
About the number 81:
- 81 has more than two factors which are 1,3, 9, 27and 81 and hence it is the composite number.
- 81 is the odd composite number and it is the perfect square also.
- If we divide 81 by 1, 3, 9, 27 and 81 then we get remainder as zero. Hence, 1, 3, 9, 27 and 81 are the factors of 81.
Note:
- 81 is the perfect square.
- Factors of 81: 1, 3, 9, 27 and 81
- Prime factors of 81: 3
Conclusion:
- 81 is the composite number which has factors 1, 3, 9, 27and 81.
- And hence, 81 is not the prime number.
Multiple Choice Questions:
1) 81 is a
a) odd number
b) Prime number
c) Composite number
d) Both a and c
Ans: d) both a and c
2) The prime factors of a composite number 81 are
a) 1
b) 3
c) Both a and b
d) 811
Ans: b)3
3) 1 is the not prime factor of 81 because
a) It is the prime number
b) 1 is neither prime nor composite number
c) Both a and b
d) Given statement is false
Ans: b) 1 is neither prime nor composite number