Monday, May 5, 2008

Subtractions, a primer...

I was in Taman Medan Jaya, Klang, on Saturday for a preview of our program, especially Qmaths. Its always a good feeling, especially if the kids and their parents show up and take part.

I had finished the "all of nine, last of ten" formula when one of the parents asked: "What if the number to be subtracted from (edit: the minuend, if you must know) is not 100 or 1000 or whatever, but a complex number, like 4,321?"

OK, I said. Lets figure that out.

Lets say we are trying to find the difference between 1,234 and 4,321:

Step 1:
Subtract 2,000 from 4,321. Why? Because 2,000 is the nearest thousandth number and larger then 1,234. If the subtrahend (thats the name we give to 1,234 in our example here) is say is only 234, then it is not 2,000 but 300. Get it? Anyway, we get 2,321 as our answer.

Step 2:
Using "All of nine, last of ten" we subtract 234 out of 1000. Easy aint it?

Step 3:
Add 2,321 and 766! Thats all there is to it!


No comments: