secrets-of-mental-math-malestrom

4
Secrets of Mental Math
Absolutely. For instance, for the problem 314 11, the
answer still begins with 3 and ends with 4. Since 3 1 4
, and
1 4 5
, the answer is 34
5
4. But we’ll save larger problems
like this for later.
More practically, you are probably saying to yourself,
“Well, this is fine for multiplying by elevens, but what about
larger numbers? How do I multiply numbers by twelve, or
thirteen, or thirty-six?”
My answer to that is, Patience! That’s what the rest of the
book is all about. In Chapters 2, 3, 6, and 8, you will learn methods
for multiplying together just about any two numbers. Better
still, you don’t have to memorize special rules for every number.
Just a handful of techniques is all that it takes to multiply numbers
in your head, quickly and easily.
SQUARING AND MORE
Here is another quick trick.
As you probably know, the square of a number is a number
multiplied by itself. For example, the square of 7 is 7 7 49.
Later, I will teach you a simple method that will enable you to
easily calculate the square of any two-digit or three-digit (or
higher) number. That method is especially simple when the
number ends in 5, so let’s do that trick now.
To square a two-digit number that ends in 5, you need to
remember only two things.
1. The answer begins by multiplying the first digit by the next higher
digit.
2. The answer ends in 25.