Class 8 Maths – Chapter 7
Cubes and Cube Roots

NCERT Questions & Answers (Student Writing Style)

Q1. Find the cube of the following numbers:

(a) 2    (b) 5    (c) 10

Answer:

(a) 2³ = 2 × 2 × 2 = 8

(b) 5³ = 5 × 5 × 5 = 125

(c) 10³ = 10 × 10 × 10 = 1000

Q2. Find the cube root of the following numbers:

(a) 27    (b) 64    (c) 125

Answer:

(a) ∛27 = 3

(b) ∛64 = 4

(c) ∛125 = 5

Q3. Is 216 a perfect cube? Find its cube root.

Answer:

216 = 2 × 2 × 2 × 3 × 3 × 3
Grouping the factors in three:
= (2 × 2 × 2)(3 × 3 × 3)

∛216 = 2 × 3 = 6

Therefore, 216 is a perfect cube.

Q4. Find the smallest number by which 128 should be multiplied to get a perfect cube.

Answer:

128 = 2 × 2 × 2 × 2 × 2 × 2 × 2
= 2⁷

To make groups of three, we need two more 2s.

Smallest number = 2 × 2 = 4

Q5. Find the cube root of 729.

Answer:

729 = 3 × 3 × 3 × 3 × 3 × 3
= (3 × 3 × 3)(3 × 3 × 3)

∛729 = 3 × 3 = 9

Q6. State whether the following numbers are perfect cubes:

(a) 343    (b) 400    (c) 512

Answer:

(a) 343 = 7³ → Perfect cube

(b) 400 → Not a perfect cube

(c) 512 = 8³ → Perfect cube

⭐ Exam Writing Tips

• Write steps clearly
• Use prime factorisation neatly
• Underline final answers

📘 Prepared by Shaktimatha Learning | Class 8 Maths