secrets-of-mental-math-malestrom

Likewise in the following example:
The Tough Stuff Made Easy: Advanced Multiplication 191
538
346
540 346 186,840
2 346 692
186,148
(540 2)
(346 6 9 10)
When-All-Else-Fails Method
When all else fails, I use the following method, which is foolproof
when you can find no other method to exploit the numbers.
In the when-all-else-fails method, the 3-by-3 problem is
broken down into three parts: a 3-by-1, a 2-by-1, and a 2-by-2.
As you do each computation, you sum the totals as you go.
These problems are difficult, especially if you cannot see the
original number. In my presentation of 3-by-3s and 5-by-5s, I
have the problems written down, but I do all the calculations
mentally.
Here’s an example:
851
527
500 851 425,500
27 800 21,600
447,100
27 51 1,377
448,477
In practice, the calculation actually proceeds as shown below.
Sometimes I use the phonetic code to store the thousands digits