These kind of tricks are pretty handy, and I don't know why I wasn't taught them back in school, growing up in the calculator generation. My father could do all

These kind of tricks are pretty handy, and I don't know why I wasn't taught them back in school, growing up in the calculator generation. My father could do all kinds of math in his head, which was just as well since he was a mathematician, but couldn't explain how he did it, he just "knew" the answer. I taught myself some tricks after the fact, the rest is just practice I think. Some examples: Multiply any two digit number by 11 easily: Using 62 as an example. Separate the two digits (6__2). Notice the gap between them Add 6 and 2 together (6+2=8) Put the resulting 8 in the gap to get the answer: 682, 62x11=682. If the result of the addition > 9, put the least significant digit in the gap and carry the most significant digit. This can be expanded to multiply any number by 11 in your head. Even really easy/obvious tricks are useful, e.g: To quickly multiply any number by 5, divide the number in two and then multiply it by 10. Very quick to do in your head.