Funny, I don't feel 8 years older....
But I just realized that a few weeks back marked the 8th anniversary of this blog (...geeez, I've never done anything for 8 years!), started at a time when most didn't even foresee America's spiral to authoritarianism coming. In any event, I'll commemorate the anniversary by simply re-running verbatim two of the posts from that very first month (the 2nd one is an old favorite to pose to young people... or, anybody):
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1) Try this exercise, I've copied directly from another book:
"Answer the following questions as fast as you can:
-2 + 2 = ?
-4 + 4 = ?
-8 + 8 = ?
-16 + 16 = ?
Now quick! Pick a number between 12 and 5. Got it?
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The number you picked is 7, isn't it?"
....I succumbed to this piece of 'mindreading' when I read it in Stanislas Dehaene's 1997 "The Number Sense: How the Mind Creates Mathematics." Did you?
He calls this a "demonstration of the automaticity of arithmetic memory" and explains it thusly:
"How did I read your mind? The mere presentation of the numbers 12 and 5 seems enough to trigger an unconscious subtraction 12 - 5 = 7. This effect is probably amplified by the initial addition drill, the reversed order of the numbers 12 and 5, and the ambiguous phrase 'between 12 and 5' that may incite you to compute the distance between the two numbers. All these factors conspire to enhance the automatic activation of 12 - 5 up to a point where the result enters consciousness. And you believed that you were exercising your 'free will' when selecting a digit!"
I'm not sure I find Dehaene's explanation completely satisfactory... but, I can't argue with the effect, which I did fall for.
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...and then this, from polymath Cliff Pickover:
2) The 3 jungle spiders.... a riddle lifted directly from chapter 9 of Clifford Pickover's "Wonders of Numbers":
"Dr. Googol was in a Peruvian rain forest, 15 miles south of the beautiful Lake Titicaca, when he dreamed up this tortuous brain boggler. A month later, while in Virginia, Dr. Googol gave this puzzle to all CIA employees to help them improve their analytical skills.
" Three spiders named Mr. Eight, Mr. Nine, and Mr. Ten are crawling on a Peruvian jungle floor. One spider has 8 legs; one spider has 9 legs; one spider has 10 legs. All of them are usually quite happy and enjoy the diversity of animals with whom they share the jungle. Today, however, the hot weather is giving them bad tempers.
" 'I think it is interesting,' says Mr. Ten, 'that none of us have the same number of legs that our names would suggest.'
" 'Who the heck cares?' replies the spider with 9 legs.
"How many legs does Mr. Nine have? Amazingly, it is possible to determine the answer, despite the little information given."
answer below:
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Mr Nine has 10 legs... (Mr. Ten CAN'T have 10 legs, same as his name, and can't have 9, since the spider with 9 replies to him; therefore he must have 8 legs... from there you can likely solve the rest.)
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