This is my last posting on this.


In article ,
Martin wrote:

Tell us about your tricks, Nick? I am sick of supermarket tricks :-)

I did. zx8 = 8x7 = 7x(4+4) = 7x7 = 10*7-3*7 and more. Also using
factorisation, so 44x75 = 11*(4*25)*3. Make a habit of that sort
of thing, and you will soon develop your own collection.

Also, using iteration (usually binary chop or interpolation) to do
division, square and cube roots etc.

Make a habit of such tricks and you will soon develop your own
suite. But mental arithmetic is no longer taught.


In article , Sacha wrote:

It's the learning by rote and repetition wot dunnit, imo.

Quite a few people can't do that at all - I never could and, as I say,
that was a punishable offence.

Then they started asking me what was the
'product' of 7 and 9 and I had no idea if they were adding it, dividing
it or multiplying it. Why couldn't it have remained "what's 7 times
9"? (Grump over) ;-)

Grin :-) Yes, if you don't know, it's not obvious. It's the result
of multiplying them.


In article ,
Mike Lyle wrote:

On the matter of multiplication tables, I didn't learn mine until
I was well into my teens, and 7x8 was always my bugbear - however,
I could work out the answer fast enough that the teachers never
realised, so I never got punished for it (sic). 7x8 = 2 x 7x4
or 7x8 = 7x7 + 7.

I think I do the last one, (7x7)+7

I suffer, too. I'm inclined to think an uncertain memory of 7x8 is so
widespread that there must be an identifiable cause: perhaps the
proximity of 6x9 has a sort of "twister" effect a little like a
tongue-twister?

I don't know the reason, but it does seem to be a widespread blind
spot. It would make an interesting research topic in psychology.



Regards,
Nick Maclaren.