Multiplication Strategies for Nines

Multiples of Nines
Look for patterns.
A.  For every multiple of 9, the digit in the tens column increases by one ten, while the digit in the ones column decreases by one:
9x2=18
9x3=27
9x4=36
9x5=45
9x6=54
9x7=63
9x8=72
9x9=81

B.  No matter what you are multiplying by 9, as long as it is between 1 and 9, the two digits of your answer will always add up to 9.

C.  Last pattern:
All the possible answers have reverse answers.
1x9    9x10
2x9    9x9
3x9    9x8
4x9    9x7
5x9    9x6