Category Archives: Probability

Q: How many samples do you need to take to know how big a set is?

The Original Question Was: I have machine … and when I press a button, it shows me one object that it selects randomly. There are enough objects that simply pressing the button until I no longer see new objects is … Continue reading

Posted in -- By the Physicist, Combinatorics, Math, Probability | 4 Comments

Q: How do we know that everyone has a common anecestor? How do we know that someone alive today will someday be a common ancestor to everyone?

The original question was: From biology and genetics we know that any group of living organisms had a mitochondrial most recent common ancestor (mitochondrial Eve): a female organism who lived in the past such that all organisms in this group … Continue reading

Posted in -- By the Physicist, Biology, Evolution, Probability | 3 Comments

Q: When “drawing straws” is it better to be first or last?

Physicist: As long as the person who cut the straws: 1) takes the last remaining straw and 2) has a decent poker face (or doesn’t know which is which), then it’s completely fair.  If they have a bad poker face, … Continue reading

Posted in -- By the Physicist, Math, Probability | 5 Comments

Q: If a long hot streak is less likely than a short hot streak, then doesn’t that mean that the chance of success drops the more successes there are?

One of the original questions was:  I understand “gambler’s fallacy” where it is mistaken to assume that if something happens more frequently during a period then it will be less frequently in the future.  Example:  If I flip a coin … Continue reading

Posted in -- By the Physicist, Math, Probability | 12 Comments

Q: If the number of ancestors you have doubles with each generation going back, you quickly get to a number bigger than the population of Earth. Does that mean we’re all a little inbred?

Physicist: In a word: yes.  But it’s not a problem in large populations. The original questioner pointed out that in the age of Charlemagne (more or less when everybody’s 40-greats grandfolk were living) the world population was between 200 and … Continue reading

Posted in -- By the Physicist, Biology, Evolution, Probability | 12 Comments

Q: If you flip a coin forever, are you guaranteed to eventually flip an equal number of heads and tails?

The original question was: Lets say we have a fair coin that is flipped a hundred times and at the end of the trial there have been 40 tails and 60 heads. At this time there have been 20 more heads than … Continue reading

Posted in -- By the Physicist, Math, Probability | 22 Comments