# Category Archives: Combinatorics

## Q: How is radiometric dating reliable? Why is it that one random thing is unpredictable, but many random things together are predictable?

The original question was: Suppose there is a set of variables whose individual values are probably different, and may be anything larger than zero. Can their sum be predicted? If so, is the margin for error less than infinity? This … Continue reading

## Q: What are Feynman diagrams, how are they used (theoretically & practically), and are there alternative/competing diagrams to Feynman’s?

Physicist: Feynman diagrams are primarily a way to keep track of what you’re doing.  Physicists aren’t geniuses or anything, and they get distracted pretty easily. When you’re trying to calculate the probability of a particular particle interaction you’ll find yourself … Continue reading

## Q: What’s the chance of getting a run of K or more successes (heads) in a row in N Bernoulli trials (coin flips)? Why use approximations when the exact answer is known?

The original question was: Recently I’ve come across a task to calculate the probability that a run of at least K successes occurs in a series of N (K≤N) Bernoulli trials (weighted coin flips), i.e. “what’s the probability that in … Continue reading

## Q: How do I count the number of ways of picking/choosing/taking k items from a list/group/set of n items when order does/doesn’t matter?

Mathematician: Suppose that we have a list containing three items, {A,B,C}, and we want to know how many different ways there are of choosing two items from this list. If we care about the order that items are selected from … Continue reading

Posted in -- By the Mathematician, Combinatorics, Math | 10 Comments