Let’s do this by examples

Find cube root of 857375.

 

Step 1:

Make group of 3 digit, starting from right

43.jpg

 

Step 2:

The unit digit of cube root will be

Unit digit of cube root of 857375 = Unit digit of cube root of 375.

 

Since 375 ends in 5, it’s cube root will end in 5.

(As 5 3  = 12 5 , 12 5 3 = 337 5 )

 

∴ Unit digit of cube root = 5

44.jpg

 

Step 3:

Now, for second group.

  8 5 7

 

We note that

  9 3 = 729

    & 10 3 = 1000

 

So,

    729  < 857 < 1000

       9 3 < 857 < 10 3

 

∴ We take smaller number

So, 9

We put 9 in ten’s place of cube root

45.jpg

 

Find cube root of 658503.

Step 1:

Make group of 3 digit, starting from right

46.jpg

 

Step 2 :

The unit digit of cube root will be

Unit digit of cube root of 658503 = Unit digit of cube root of 503

 

Since 503 ends in 3, it’s cube root will end in 7.

(As 7 3  = 34 3 , 1 7 3  = 491 3 )

 

∴ Unit digit of cube root = 7

47.jpg

Step 3:

Now, for second group.

  6 5 8

 

We note that

      8 3 = 512

  & 9 3 = 729

 

So,

    512  < 658 < 729

       8 3 < 658 < 9 3

 

∴ We take smaller number

So, 8

We put 8 in ten’s place of cube root.

48.jpg

∴ Cube root of 658503 = 87

  1. Chapter 7 Class 8 Cubes and Cube Roots
  2. Concept wise
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Davneet Singh
Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 8 years. He provides courses for Maths and Science at Teachoo. You can check his NCERT Solutions from Class 6 to 12.