#incomplete

Multiplying by 11

Take the first and last digit and add them together and insert that in the middle of the original digits

Example: $$34\cdot11 = 374$$ If the addition adds up into the next digit carry over the value $$37 \cdot 11 = 407$$ $$ 38 \cdot 11 = 418 $$

Squaring numbers

You can quickly square any number

for example

Multiplying two two-digit numbers

A more formal definition for nerds