Anybody that knows me knows I'm horrible in math. But then, most people don't even know who I am on this blog so what does it matter??? LOL
Anyway, I found this really cool math trick that I thought I might pass along, because even I could do it!! I took this from Curious Math and if I can do it anyone can. It was posted by a person named kayer35.
Got 5 minutes to spare? That's all the time you need to learn how to quickly multiply two numbers from 11 to 19 in your head.
With this trick, you will be able to multiply any two numbers from 11 to 19 in your head quickly, without the use of a calculator.
I will assume that you know your multiplication table reasonably well up to 10x10.
Lets try 15 x 13.
1. Always place the larger number of the two on top in your mind.
2. Then draw the shape of Africa mentally so it covers the 15 and the 3 from the 13 below. Those covered numbers are all you need.
3. Now add 15 + 3 = 18
4. Add a zero behind it (i.e., multiply by 10) to get 180.
5. Multiply the covered lower 3 by the single digit above it, in this case the "5" (3 x 5 = 15)
6. Add the products from steps 5 and 6 to get your answer. 180 + 15 = 195.
That's it! Wasn't that easy? Practice it on paper first!