I know how to get the x = (a-1)/(a+b-2) but, I am a little confused how to get the (x+a)/(n+a+b-2) ???
Hi ping2002, Instead of having a Beta distribution with parameters alpha and beta, we now have a Beta distribution with parameters alpha + x and beta + n - x So, swap alpha for alpa + x and swap beta for beta + n - x and you'll get the formula you are looking for. This idea of swapping letters about (working out which bit is which) is incredibly important in Subject CT6. Sometimes it can get a bit confusing, we can have a PDF where the random variable is lambda (so this is like x in all the PDFs in Tables) but when you look up a PDF in Tables, eg Gamma distribution the letter lambda might also happen to be there! :-( You have to be careful not to confuse the letters just because they both happen to be lambda! So this needs a bit of practice, Good luck! John
