## Chapter 7 Cubes and Cube Roots Exercise 7.1

**Question 1: Which of the following numbers are not perfect cubes?**

(i) 216

(ii) 128

(iii) 1000

(iv) 100

(v) 46656

Answer:

(i) 216

(ii) 128

(iii) 1000

(iv) 100

(v) 46656

Answer:

(i)

(ii)

(iii)

(iv)

(v)

**Question 2: Find the smallest number by which each of the following numbers must be multiplied to obtain a perfect cube.**

(i) 243

(ii) 256

(iii) 72

(iv) 675

(v) 100

Answer:

(i)

(i) 243

(ii) 256

(iii) 72

(iv) 675

(v) 100

Answer:

(ii)

(iii)

(iv)

(v)

**Question 3: Find the smallest number by which each of the following numbers must be divided to obtain a perfect cube.**

(i) 81

(ii) 128

(iii) 135

(iv) 192

(v) 704

Answer:

(i) 81

(ii) 128

(iii) 135

(iv) 192

(v) 704

Answer:

(i)

(ii)

(iii)

(iv)

(v)

**Question 4: Parikshit makes a cuboid of plasticine of sides 5 cm, 2 cm, 5 cm. How many such cuboids will he need to form a cube?**

Answer:

Answer:

Volume of cuboid × number of cuboids = volume of cube

lbh × number of cuboids = (edge)³

5 × 2 × 5 × (x) = (edge)³

5 × 2 × 5 × (5 × 2 × 2) = (edge)³

5 × 2 × 5 × 20 cuboids = 5³ × 2³

Therefore, Parikshit require 20 cuboids to make a cube.

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