Cubes and Cube Root Exercises-Class VIII

1. Which of the following numbers are not perfect cubes?

(i) 216

Answer: 216 = 2 x 2 x 2 x 27

= 2 x 2 x 2 x 3 x 3 x 3

As number of 2s and 3s is 3 in the factorization so it is a perfect cube.

(ii) 128

Answer: 128 = 2 x 2 x 2 x 2 x 2 x 2 x 2

Number of 2s is 7 and 7 is not divisible by three so 128 is not a perfect cube

(iii) 1000

Answer: 1000 = 2 x 2 x 2 x 5 x 5 x 5

Number of 2s and 5s is 3 each so 1000 is a perfect cube.

(iv) 100

Answer: 100 = 2 x 2 x 5 x 5

Number of 2s and 5s is 2 each and not 3 so 100 is not a perfect cube.