Not for 14 times 12, as that is (13+1) times (13-1). 'everybody' knows 1^2 = 1 and 13^2 = 169, so 14 times 12 = 169 - 1 = 168.

Yes, I process everything in 10% as well. 15% tip on $34? 10% = $3.4 so half of 3.4 is 1.7, combine them for $5.10.

Sometimes. Or to multiply by 25, multiply by 100 and divide by 4. I always meant to study the trachtenberg method but never got around to it

Similar here, but based on memorization. Since I know twelve squared ((12 * 12) = 144) by rote, the rest is easy.

  14 * 12 = (12^2) + (12*2) = 168

I tend to use the tens as well, but in this case I would have used the 12*12 + 24 trick. I also use some of the others listed here, so it makes me happy to know there are people like me out there.

I do this sometimes.

Sometimes I refactor at first:

    14*12=28*6=56*3=56*2+56=112+56=168

or

    14*12=7*8*3=21*8=160+8