Sab Theek Ho Jayega !

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Kochi / Ernakulam, Kerala, India
A Doctor who loves to Live, Love and Laugh with the World! Absolutely crazy about Cricket ! Other Qualifications: A Tired Bathroom Singer, Retired Gully Cricketer and Satire Writer !

Thursday, April 5, 2012

Solving the 9th Wonder !

Multiplying any number ending with 9 is a big 'scare crow' for kids in primary school. It becomes virtually a non-issue if we approach it as a process of addition and subtraction rather than multiplication. Once again unfortunately, people shut their minds even before we count from 1 - 9.

My daughter used to do the same till I made her use a method that has eradicated the fear of multiplication from her mind. She now enjoys doing it in the mind and she is always correct. But she still hasn't exorcised the 'Ghost' from her mind and wants to check if her answer is correct. She will be confident with time.

So what do we do ?

Simple. Let us take the simplest of numbers ending from 9, that is 19. Most kids would know the multiplication table by heart. But is that necessary ? I have never found that necessary. I approach it as adding 19 as many times as I am supposed to multiply. So 38, 57, 76 and there goes the table.

Often kids get stuck on reaching 7, 8 and 9. That is where the realization comes that it actually is easier to add and delete than do a table. I do it this way.

19 is 1 less than 20. 
We all can have multiples of 20 easily because 20 is nothing but 2 x 10. 
So just check this method. 
I do 20 x 9 = 180. 
When it comes to 19 x 9, that means it actually is one 9 less than 20 x 9. 
So just delete 9 from 180. 
That means 19 x 9 = 171. 
That is it !

Let us move to larger numbers.

Let us take 89 x 7. 
What I do is 90 x 7 = 630. 
We know 89 x 7 is one less times 7.
So just delete 7 and that means 623.

Let us take another example of 99 x 8. 
100 x 8 = 800. 
Minus 8 means the answer is 792. 
The riddle solved, in the mind. 

No paper, no pencil and in no time. And of course no tension !

Dr. Punned-it

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