Thread:KittehWizard/@comment-6247700-20130201021838

thought it would be better to post on your wall, rather than take the diamond dragon breeding even further off track...

basically the equation comes from the following logic statement:

What is the chance of getting a head on the first flip? 50%

If I didn't get a head on the first flip (the other 50%), then what's the chance I get a head on the 2nd flip? 50%.... however the chance of this exact event (being a tail followed by a head) is only 25% (being 50% times 50%)

another way to look at it... is to use a tree diagram:



so Chance of gettin at least 1 head in 2 throws = 50% (being the chance of getting the head on the first go) + [50% (because you got a tail on the first go) x 50% (being the chance of getting a head on the 2nd go)]

hope this helps :D I've never been good at teaching, I've got other methods of working this out, but don't want to bore you 