
Multiplying two numbers whose difference is
10 and unit digit is 5 )
Example  25 * 35
First categories in two parts
In first part
2, 3: big number square subtract 1
3^2  1 = 9  1 = 8
In second part
Always put 75
So answer became 875
Example  155 * 165
= 256  1  75
= 25575