Do you know any good mental math techniques ?

Question

Or websites which teach these techniques you may post.

I appreciate it, thanks so much.

Answer 1

One of my favourites is to approximately calculate multiplication and then use a smaller addition/subtraction to make it exact.

So: 21 X 372

I would do ... 20 X 372 (which is easy ... 600..., no 744 and then tack on a 0 to the end: 7440) and then ADD another 372 to make 7812)

Note that the 372 X 2 calculation was done from left to right rather than the traditionally taught right to left - 2X2 is 4, 2X7 is 14 so write down 4 carry 1, 2X3 is 6 plus 1 is 7 ...

I did that as 2X3 = 6 but ther'll be an extra 1 from the 2X7 so think 7...4...4... add the 0

Have a look at this wiki page for a few other techniques.

Answer 2

mental math trick:

factor

it seems hard to do 12*14 in your head but break it up to 6*2*2*7 and get 42*4. now, you can get 168.

Answer 3

I just have to back Orinoco up - Left-to-right is the way to go if you're doing math in your head.

Answer 4

alway's add in even numbers always go in multipules of 10

Answer 5

vedicmaths