Question

Which of these is/are not a perfect cube?

• A. 343
• B. 1331
• C. 512
• D. 81

Answer 1

Answer: (C), (D)

The correct options are
C

512

D

81

81 is not a perfect cube.

By prime factorization, 81 = $3^4$

To be a perfect cube we need the factors to be multiplied 3 times, that is the cube of a number is the number raised to the power 3.

Similarly,

256 is also not a perfect cube.

By prime factorization, 256 = $2^8$. To become a perfect cube it has to be multiplied by 2 again. i.e. $2^9=512$ is a perfect cube of 8.

343 and1331 are the perfect cubes of 7 and 11 respectively.