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Geek Brain Teasers
muce writes "A few days ago my cube mate entertained a lot of us engineers by presenting us with the famous Monty Hall problem. That problem sparked a day of strong debates, coding simulations, and ramped writing of equations on whiteboards. Since then we've been thirsting for more good geeky mathematical brain teasers to pass the time at work. Does anybody know of any good ones like the Monty Hall problem, or by chance is there a web page with a collection of them?"
I posted this lat time Ask /. had a puzzle of boring Sunday a while back.
Three smart kids are on a beach and all have mud on their foreheads. An old man comes over to them and asks for each of them to look at *both* their friends, and should one *or* both of their friends have mud on their foreheads, they should raise their hands. All three kids look at both of their friends, and seeing mud on both of their friends heads, they raise their hands.
The old man then offers a dollar to anyone who can answer his next question, and prove it. He asks if any of the kids know that they do, or do not, have mud on their foreheads, and if they can prove it. The kids look at each other and are bewildered for a bit. Suddenly, one of them screaches, "Oh!" and raises his hand. He then explains to the old man how he must have mud on his forehead and explains his reasoning. As his reasoning was excellent, the old man gives him the dollar.
What was the boy's reasoning?
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ticks = jiffies;
while (ticks == jiffies);
ticks = jiffies;
Have you read my journal today?
Let's assume without loss of generality that you pick the first digit. That rules out cases 4 to 7. Knowing there's at least a 1 rules out case 0. The cases left are 001, 010 and 011. Therefore the odds that there are two 1's is 1/3.
Get it now?
sub f{($f)=@_;print"$f(q{$f});";}f(q{sub f{($f)=@_;print"$f(q{$f});";}f});
As a side note, at one time I heard an explanation of her world record IQ that makes me discount her as the world record holder.
Supposedly IQ scores depend on the sample size taking the test. If a relatively small number of people take the test, even scoring a perfect score can only rate an IQ a few points above the average.
So the story I heard is that the test she set the record on was one of the most widely given standardized IQ tests. I believe she is solidly in the "baby boomer" set and I think this was a school test given years and years ago.
Since no test since then has been given to more people, even a perfect score on every IQ test since then wouldn't result in breaking her record.
Of course, that's just the information I heard. It could be wrong, but it does sound plausable.