So, You Think You Can't Do Mental Arithmetic?

How many times have you heard someone say 'I can't do mental arithmetic'?
Perhaps it is something that you have said yourself many times . . . I know I have!
The problem, I have found, is not 'I can't do mental arithmetic' but 'I don't know how to do mental arithmetic'.
This certainly was the case for me.
Let me show you what i mean.
If I were to ask you to multiply 43 x 11. Would you be able to do it? How long would it take you to do it?
If you asked me that 1 year ago, I would have said 'I can do it but it will take me a while'. You see, like many people, I believed that I couldn't do mental arithmetic.
Now, let me show you how to do 43 x 11 in your head in less than 1 second (it will take you less than 1 second once you know how to do it).
1. separate the 4 and the 3 thus: 4 __ 3 (because we are going to put a number in between the 4 and the 3),
2. add 4 + 3 to get: 4 + 3 = 7,
3. place the 7 between the 4 and the 3 to get: 4 7 3,
That is your answer: 43 x 11 = 473
How easy is that?
Practice on the following and see how quickly you can do them in your mind:
- 23 x 11 = (23 x 11 = 253)
- 18 x 11 = (18 x 11 = 198)
- 71 x 11 = (71 x 11 = 781)
If I were to ask you now, what is 27 x 11? You would be able to work it out in your head in less than 1 second and tell me: 297.
Congratulations! You have gone from 'I can't do mental arithmetic' to 'Gee, that was easy!'.
The thing about mental arithmetic is: the problem is not 'I can't do mental arithmetic' but 'I don't know how to do mental arithmetic'.
There are many such tricks to doing mental arithmetic and once you know them, you will be amazed at the type of mental arithmetic calculations you will be able to do in you head in less than 1 second:
- divide by 5 eg. 42 / 5 = ?
- multiply by 5 eg. 68 x 5 = ?
- square a number that ends in 5 eg. 45 x 45 = ?
- and so on . . .
So, take heart! You are not as 'dumb' as you think. You can't do mental arithmetic simply because you were never shown how to do it . . . and not because you can't!
Serge M Botans