Actually, it's not all that weird -- it just cross-circuits most people's
brains because of the way they are taught to read & add numbers [right to
left, as opposed to left to right in the case of words in sentances...]

If you mentally keep track of it --IN THE ORDER PRESENTED-- you should be
thinking as follows:

   one-thousand
   one-thousand forty
   two-thousand forty
   two-thousand seventy
   three-thousand seventy
   three-thousand ninety
   four-thousand ninety
and then the trip-up -- adding ten to four-thousand ninety, which causes a
carry into the hundreds category.  because you've been mentally see-sawing
between adding digits in the "thousands" range with those in the "tens"
range, you're mentally prepared to ignore the "hundreds" range entirely.

A similar trick is ask a person to spell the following words:

   joke
   poke
   toke
   folk

[and/or any other words that end with or rhyme with "oke" or "olk"]

then ask them to tell you [or spell] the white part of an egg -- a fairly
large sample will respond with "yolk"  (which, of course, is wrong -- the
yolk is the YELLOW part...)

> -----Original Message-----
> From: Brian Duncombe [mailto:[log in to unmask]]
> >  > > >>>   This riddle must be Done In Your Head and Not
[...]
> > > > >>>Take 1000 and add 40 to it. Now add another 1000.
[...]