Monday, April 7, 2008

mental maths

Hi everybody let us see this week how the number 9 can be multiplied with numbers from 11 upto 99. Let me start with the example 42 X 9 = ? Please don’t use the calculator because your brain itself a calculator!!!. Just follow the steps below to multiply the numbers.

42 X 9

(4+1) – 42 X (9+1)


42 – 5 X (10-2)

378

that’s it the answer is 378 now pls check with calculator .

4 comments:

Les said...

42 X 9

I must be thick - cos I just don't get the explanation.
If we take the example of 42 x 9 I would simply say 2 x 9 = 18; 40 x 9 = 360; 360 + 18 = 378

You restate this as:
(4+1) – 42 X (9+1)

Where does (4+1) come from?
Where does (9+1) come from?
How does this become 42 – 5 X (10-2)?
Anyway 42 - 5 = 37
(10 - 2) = 8
37 x 8 = 56 + 240 = 296
Clearly this is not 378
I do recognise that you have the numbers 37 & 8 which are the components of 378...

Please can you explain so that I understand

ozkarin0 said...

not sure that is a good trick since there is no good explanation. where is this 4+ 1 and 9+1 comes from?

Mukund said...

There is no explanation for the answer. It required to understand the procedure

GADALRAB said...

SORRY IT NEED MORE EXPLANTION.