Teacher: 60 seconds… You have exactly 60 seconds to find the cube of 24! And your time starts now!
Ana: Ma’am answer is 13824.
Teacher: Well done Anna! Can you tell the
class from where you learned this trick?
Ana: Yes sure. I have learnt this trick from Letstute which is an e-learning
platform. They have explained this trick in a very easy manner.
To find the cube of 24. The first step is to draw 4 blank spaces. In the first blank space,
we write the cube of the first digit,
i.e. 2’s cube 8 and in the last part write the cube of the second digit i.e. 4’s cube 64.
Now, the next step may get a little tricky, so make sure to pay close attention. First,
we’ll multiply all the digits together i.e. 2*4*3, which gives us 24. Now we’ll multiply this 24 with
each digit of the original number whose cube we have to find. So, multiply 24 by 2 to fill the
blank space over here. And multiply 24 by 4 to fill the 3rd blank.
Stay with me as we are almost done. Here in the first part add three zeros after the number,
in the second add two and in the third part add one zero. And for the fourth part,
we do not need to make any changes! Now, it’s time for the last step,
which is to simply add all the four numbers. And here is our answer - 13824. The cube
of 24 is 13824. if you are not so sure that your answer is correct,
you can use a calculator and crosscheck it. Show calculator and calculate cube of 24.
See, finding the cube of any number is this simple. And all we have to do is remember a
cube of numbers from 1 to 10 only. Now, I want you to use this technique to find the cube of 72.
So be ready with your pen and paper.
So, I hope you remember the first step! Yes, make 4 blank spaces and write a cube of 7 over here
and a cube of 2 over here. Now, multiply all the three digits, which will give us
42. Now go ahead and multiply 42 by 7 which equals 294. For step
three, we’ll multiply these two together (42 x 2). And what was the last step? Yes,
bring in that army of zeros in the picture! And the last step is to add all the 4 numbers. So,
there you go, the cube of 42 is 373248! Yes, yes, get that calculator and cross check the answer.
Now you must be thinking, what if we want to find the cube of a three digit number?
So for a three digit number, we don’t have to do anything different. Now, let’s assume we’re trying
to find the cube of 125, so, to find the cube of 125, we first separate the number 125 as 12 and 5,
and use the same trick which we just learnt to find the cube of two digit numbers.
I hope you understood this trick well! But do you all know the origin of this
trick? It has something to do with a very famous mathematical formula - (a+b)3. How?
Well, now assume that ‘ab’ is a two digit number, and try to find its cube using this trick,
and the answer you’ll get is this. Write the formula on screen (a+b)3=
a3 +3a2b+3ab2+b3. Besides the above image Now, I want you to tell me in the comments
if you can find the cube of these two numbers in less than a minute or not
Remember that to solve it faster all you require is practice and perseverance.
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