Friday, August 1, 2014

BEST TRICK TO CALCULATE THE CUBE ROOT OF A NUMBER:-

Step 1

Please Remember the first 9 Cubes
1 –> 1
2 –> 8
3 –> 27
4 –> 64
5 –> 125
6 –> 216
7 –> 343
8 –> 512
9 –> 729

Step 2

Remember the last digit (unit digit) of each cubes. List with unit digits this time.
1 –> 1
2 –> 8
3 –> 7
4 –> 4
5 –> 5
6 –> 6
7 –> 3
8 –> 2
9 –> 9

Now see how to solve cube roots faster.

Q.1) Find out the cube root of 42875.

Here is how to solve this question.

The first step is to divide the number into 2 parts by separating the last 3 digits. So, we get 42 & 875 as the two parts of the number.

Now, take the first part and find the largest cube contained in the first part i.e. in 42 = 27 (which is the cube of 3). The next cube i.e. 64 (cube of 4) is larger than 50. Now, as 27 is the cube of 3, your ten’s part of cube root would be 3. [This is why we memorized the cubes]

The next step is to take the last digit of the number, which in this case is 5. Which number’s cube had 5 as the unit digit? 7… right?? (5*5*5=625) Hence, 5 is the unit digit of your solution. [This is why we memorized the endings]

So, your answer is 35. Try cubing 35 on a calculator to verify your answer.

Let us solve another example to show how the answer can be achieved in less than 5 seconds.

Q.2) Calculate the cube root of 474552.

By Step 1 —– We get two parts i.e. 474 and 552.

By Step 2 —– The largest cube less than 474 is 343 (cube of 7). So, ten’s digit is 7

By Step 3 —– The ending digit is 2. Hence, unit’s digit is 8. That’s it. 78 is the answer.

Practice it a bit and you would be able to solve this in even less than 5 seconds......