secrets-of-mental-math-malestrom

140
Secrets of Mental Math
You have now written the answer: 1
5
9
8
.
Let’s solve another 2-by-2 multiplication problem using the
criss-cross method:
83
6 5
5395
The steps and diagrams appear as follows:
Step 1. 5 3 15
8 3
6 5
Step 2. 1 (5 8) (6 3) 59
8 3
6 5
Step 3. 5 (6 8) 5
3
8 3
Answer: 5
3
9
5
The criss-cross method gets slightly more complicated with
3-by-3 problems.
853
762
649,986
Step 1. 2 3 6
6 5
We proceed as suggested by our pattern below:
8 5 3
7 6 2