# Cube root using ones and tens method

Using ones and tens method, we can find the cube root of any perfect cube having at most 6 digits.This method is not applicable for the number having more than 6 digits like 5832000. So,keep it in mind while using this method

Important points :

• If a number ends with digit 0,1,4,5,6 and 9 .Then ,their cube also ends with digit 0,1,4,5,6 and 9 respectively .
• Whereas, if a number ends with digit 2 or 3 .then, their cube ends with 8 and 7 respectively.

You can see in the given table :

The red box and yellow box indicates the above two conditions respectively Let’s talk about step by step procedure to calculate cube root using the ones and tens method

Step:01 Find the one’s digit of the required cube root.

Step:02 Cross out the last three-digit of the number

Step:03 Think of the number whose cube root is less than or equal to the remaining digit of the number (Digit left after Step:02)

Let’s take a number and try to find its cube root using the ones and tens method . Assumed number: 91125

Solution:

Step:01 Find the unit digit of the required cube root

Since we know 91125 is a perfect cube and its unit digit is 5 . So, its cube root unit digit will also 5.

See above table

Step:02 Cross out the last three-digit of the number Step:03 Think of the number whose cube is less than or equal to the remaining digit of the number (Digit left after Step:02)

After crossing out the last 3 digits,we have 91 as the remaining number. Now, think of a number whose cube is less than or equal to 91. 4³= 64 and 5³=125, 91 lies between cubes of 4 and 5.

So, 4 is the tens digit of the required cube root and we have already found one’s digit in step:01 i.e 5.

Hence, cube root of 91125 is 45

Examples :

Q.1 Find the cube root of 531441 using the ones and tens method

Solution:

Since,

Unit digit of 531441 is 1 . So, 1 will also be the unit digit of the required cube root

Now  strike out the last three-digit of the 531441 Remaining number = 531

Think of the number whose cube is less than or equal to 531.See above table

531 lies between cubes of 8 and 9

So, 8 is the tens digit of the cube root and we have found one’s digit i.e 1

Hence, the cube root of 531441 is 81

Practice problem

Q .Find the cube root of following number using ones and tens method

(i) 4096

(ii) 110592

(iii) 389017

(iv) 592704

(v) 5832000

(i) 16

(ii) 48

(iii) 73

(iv) 84

(v) Can’t find ,it has more than 6 digits

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