Saturday, 15 April 2017

How to Easily Find the Cube Root of a Number that is a Perfect Cube in IBPS PO Exam

Sometimes all that stands between you and the answer is the need to find a cube root. In this post we’ll discuss how to find cube roots of perfect cubes for IBPS PO Exam. 

Find the Cube Root

We are all familiar to a situation where we give up a question midway in IBPS PO Exam despite knowing the method because it involves some tedious calculations where we have to find the cube root of a number. We promise you that after reading this article, finding cube roots of perfect cubes will not be difficult anymore.
The 18th smart method in this series will ensure that you can find the cube root of a perfect cube in just 5- 10 second.
Find the Cube Root

What is Cube Root and Perfect Cube

A cube root of a number ‘x’ is a number attained when that number is multiplied with itself three time, such that a3 = x. All real numbers (except zero) have exactly one real cube root and a pair of complex conjugate cube roots.
Find the Cube Root


Example of a Question to Find the Cube Root

What is the cube root of 328509?
1) 63      2) 61      3) 69      4) 79      5) None of these

Conventional Method to Find the Cube Root

Our teachers taught us a long complicated method using long division to find the cube root of any number. We started with making groups of three digits and kept adding zeros after the decimal and then followed the difficult method of long division the thought of which also scares me now.

Smart Method to Find the Cube Root

Time to ditch that age old method and adopt a smart method for this complex calculation! This method takes about 5 seconds and you’ll be able to find the cube root in 2 steps.

In step 1 one look at the last digit of the number and explore the possible options of the cube root based on the digit.

Step 1:
In the given case the number is 328509 where the last digit is 9, which means that the cube root ends in 9

For step 2 leave the last three digits aside and find the highest number whose perfect cube comes closest to it. This number will comes in the tens place in the answer.

Step 2:
Leaving aside the last three digits of the number 328509, we have 328 and the highest perfect cube that come closest to it is 63 = 216

Step 3:
So our answer is 69

Bingo! What a sigh of relief to realize that there is a simple method to find out cube roots. 
Find the Cube Root

Watch our expert faculty explain the same!


Try to find the cube root for the following perfect cubes-

Question 1: What is the cube root of 373248?
1) 73      2) 72      3) 78      4) 79       5) None of these

Question 2: What is the cube root of 79507?
1) 43      2) 41      3) 53       4) 47       5) None of these

Do write your answer in the comments below and tell us how long it took you to find the cube root.

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Find the Cube Root


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