NCERT Solutions for Class 8 Maths Chapter 7 Cubes and Cube Roots Ex 7.1

NCERT Solutions for Class 8 Maths Chapter 7 Cubes and Cube Roots Ex 7.1, are part of NCERT Solutions for Class 8 Maths. Here we have given NCERT Solutions for Class 8 Maths Chapter 7 Cubes and Cube Roots Ex 7.1.

NCERT Solutions for Class 8 Maths Chapter 7 Cubes and Cube Roots Ex 7.1

Question 1.
Which of the following numbers are not perfect cubes?
(i) 216
(ii) 128
(iii) 1000
(iv) 100
(v) 46656
Solution.
(i) 216
ch 7.1 1

(ii) 128
ch 7.1 2
ch 7.1 3

(iii) 1000
ch 7.1 4

(iv) 100
ch 7.1 5
ch 7.1 6

(v) 46656
ch 7.1 7
ch 7.1 8

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
Solution.
(i) 243
ch 7.1 9
ch 7.1 10

(ii) 256
ch 7.1 11
ch 7.1 12

(iii) 72
ch 7.1 13
ch 7.1 14

(iv) 675
ch 7.1 15
ch 7.1 16

(v) 100
ch 7.1 17
ch 7.1 18

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
Solution.
(i) 81
ch 7.1 19
ch 7.1 20

(ii) 128
ch 7.1 21
ch 7.1 22

(iii) 135
ch 7.1 23
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(iv) 192
ch 7.1 25
ch 7.1 26

(v) 704
ch 7.1 27
ch 7.1 28

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?
Solution.
Volume of a cuboid = 5 x 2 x 5 \({ cm }^{ 3 }\).
Since there is only one 2 and only two 5’s in the prime factorization, so, we need 2 x 2 x 5, i.e., 20 to make a perfect cube. Therefore, we need 20 such cuboids to make a cube.

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