Best tricks to calculate cube roots: In the Numerical Ability section of Banking exams, calculation plays an important role to score high. Now, to strengthen it, you have to practice a lot. Practising questions will increase your speed as well as accuracy. Speed is also dependent on short tricks as we use them in the exam to save time for other questions.
In the calculation, you must know the tables till 25 at your fingertips. With this, learning squares and cubes till 25, square roots till 20 and cube roots till 10 is must. Remembering them will enhance your calculation skills. We have already shared the calculation short tricks of a square, cubes, and square roots. You can go through the tricks and prepare them well.
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In the article, we will be discussing the short tricks to calculate the cube roots of the definite cube numbers. For this, you just have to remember the cubes till 10 to apply this technique.
Cubes of the numbers (1 to 10)
| Numbers | Cubes |
| 1 | 1 |
| 2 | 8 |
| 3 | 27 |
| 4 | 64 |
| 5 | 125 |
| 6 | 216 |
| 7 | 343 |
| 8 | 512 |
| 9 | 729 |
| 10 | 1000 |
Now, do you analyze anything from the above table?
Observation 1:
| Unit digit of the numbers and their cubes is similar | |
| 1 | 1 |
| 4 | 6 4 |
| 5 | 12 5 |
| 6 | 21 6 |
| 9 | 72 9 |
| 10 | 100 0 |
So, always remember that, if you find a number who is a definite cube and carries the above-mentioned unit digits, then their cube roots will also have the same unit digits.
Observation 2:
| Numbers having the unit digit 2 will have 8 as the unit digit in the cube and vice versa | Numbers having the unit digit 3 will have 7 as the unit digit in the cube and vice versa | ||
| 2 | 8 | 3 | 2 7 |
| 8 | 51 2 | 7 | 34 3 |
Thus, keep in mind that if you find a number who is a definite cube and carries the unit digits as:
a. 2, then cube root will have unit digit as 8.
b. 8, then cube root will have unit digit as 2.
Remember the conclusions of the above observations. They will be used in the steps of calculating the cube roots.
Method to calculate cube roots of definite Cube numbers
Let us discuss through an example:
Find the cube root of a number 59319.
Step 1: Divide the number by taking 3 rightmost digits in one part and remaining digits in another part. Then, from the unit or last digit of the cube, find the unit digit of cube root number.
Here the last digit of the cube is 9. Now, as per the above observation, the numbers having the unit digit 9 have the same unit digit in their cubes and vice versa. So, the unit digit of cube root will also be 9.
Step 2: Now consider the remaining digits of the number. Then find the smaller cube number to the remaining digit and write its cube root number.
Here, remaining digits: 59.
Smaller cube to 59 is 27.
Cube root of 27 is 3.
So, cube root of 59319 is 39.
So, with the help of just two simple steps, you can find the cube root of the number.
| Cube root of 59319 | |
| 59 | 31 9 |
| 27 or (3)3 < 59 | 9 |
| 3 | 9 |
| 39 | |
Let`s have some examples to understand it better.
Example 1: Find the cube root of 91125.
| Cube root of 91125 | |
| 91 | 12 5 |
| 64 or (4)3 < 91 | 5 |
| 4 | 5 |
| 45 | |
Example 2: Find the cube root of 175616
| Cube root of 175616 | |
| 175 | 61 6 |
| 125 or (5)3 < 175 | 6 |
| 5 | 6 |
| 56 | |
Example 3: Find the cube root of 300763
| Cube root of 300763 | |
| 300 | 76 3 |
| 216 or (6)3 < 300 | 7 |
| 6 | 7 |
| 67 | |
Example 4: Find the cube root of 474552
| Cube root of 474552 | |
| 474 | 55 2 |
| 343 or (7)3 < 474 | 8 |
| 7 | 8 |
| 78 | |
Example 5: Find the cube root of 778688
| Cube root of 778688 | |
| 778 | 688 |
| 729 or (9)3 < 778 | 2 |
| 9 | 2 |
| 92 | |
In this way, you can calculate the cube roots of the definite cube numbers easily. You don't have to write all the steps in the exam. Just calculate the steps in your mind and answer quickly.
In the upcoming articles, we will be sharing the short tricks of some other topics. Stay connected and keep going with practice.
Note: Using this technique, you can find only 2 digit cube root numbers.
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