Read this from the omy. Actually this is simple algebra.(10+a)(10+b) = 100 + 10x(a+b) +a*b
or
(100-a)(100-b)=10000-100x(a+b)+a*b
I would like to share with you a more interesting way of doing 'times', which is called the Russian multiplication. What we need to do is keep halving the first no. and keep doubling the second no.
Take 19x6=114 as an example.
19 6
9 12
1 96
Add all the remaining number in the second column will give you the product.
6+12+96=114
This method can apply to any digits nos.
Take another example 19x19=361
19 19
9 38
1 304
The answer of 19x19 = 19+ 38 +304 =361
Keep reading only if you are interested. 😁
When we keep halving one number and keep doubling the other number, it will not affect the product of these 2 nos.
a/2 * 2b = a*b
However, while we keep halving the first number, we may come across an 'odd' no.
When we halve an odd number, we get a 'remainder' !
Question arises, "What is the remainder?"
So take 5x6 =30 as an example. (using primary maths model method)
Imagine 30 candies were put into 5 boxes, each box has 6 candies.
So when we halve 5 boxes, we get 2 boxes AND we have dropped 1 box, that is 6 candies.
That is to say , the no. on the second column is the remainder!
And that's why we have to cross out all the even no. row and add up the remaining nos. of the second column for the 'product' ( to pick up what we have dropped )
5 6
1 24
5x6 = 6+24 = 30
Do try it yourself and have fun!
ps. I'm not a maths expert, nor teacher / tutor. I only share what I know. It's so good if you have known already. And it's no harm to learn something new for those who don't. Thank you. 😊
