what are the shortcut techniques in mental mathematics?

Question

shortcut in in solving methematical operations such as addition,subtraction, multiplication and division

Answer 1

Well this is a simple one. When multiplying by 9 fro 1 to 10 use your hands.

first put up all 10 fingers of both hands up:
For example:
9x1 put left pinky down. You have 9fingers up 9x1=9
9x2 put left ring finger down. 1 figer up followed by 8 up, 9x2 = 18
....
etc.
This will work up to 9x10

This is a good trick to teach younger kids to multiply by 9 =D

Answer 2

Well, there are hundreds, here's an interesting one if not very common:
multiplying any number ending in 5 by itself:
25x25= take the 2, add 1 and multiply (2x3) that gives 6
then add 25 to it for 625

so 65x65 is 6x7 wth 25 at the end so 4225
105x105=11025

Answer 3

use the calculator ..........lol