Poll: the sum(7,9)

[David Vaughan]

On 16/03/2005, at 5:57, various people wrote on:

> Subject: Re: Poll: the sum(7,9)
> Reply-To: How to use Revolution <use-revolution at lists.runrev.com>
>
>
>> It's this:  How do you mentally process simple addition/subtraction
>> facts?  What actually happens in your brain to elicit 16 when you hear
>> 7+9? (for example)

It depends a bit on how complex the question. My response to "7 9 +" 
was initially the second of those originally suggested by Mark - 
pattern recognition, probably a direct consequence of his third option, 
rote learning at school. The same certainly happens instantly for 
numbers where the sum is less than 13 and very fast for others. When 
the numbers get larger, I use accumulated pattern-bits to break down 
the problem and derive an answer, which actually seems to involve an 
approximation on most parts of the number then fixing the details in 
any unconsidered digits. If it is "difficult" or I am tired then 
concrete methods start to move in to deal with it, involving 
visualising changing numbers.

However, the later question, "17 9 -" (seriously folks, over 30 years 
my thinking really has shifted to the point where RPN is as easy as and 
"more sensible" than infix) caught my attention.  The answer came 
straight away but I managed to rerun the question immediately in my 
head and think I got some glimpse of what happened, insofar as one can 
believe introspection. It went something like " 9 is one less than 10 
and I see 17 so the answer is 8". Bang. Nothing more I noticed (I 
barely caught the "and I see 17" but it had to be there) and in 
retrospect I am not quite sure I would think of it quite that way, but 
it seems to work.

cheers
David