Re: Binomial Distribution

*To*: mathgroup at smc.vnet.net*Subject*: [mg71366] Re: [mg71356] Binomial Distribution*From*: Andrzej Kozlowski <akoz at mimuw.edu.pl>*Date*: Thu, 16 Nov 2006 00:52:44 -0500 (EST)*References*: <200611151145.GAA01517@smc.vnet.net>

On 15 Nov 2006, at 20:45, Bruce Colletti wrote: > Re Mathematica 5.2 under WinXP. > > Why doesn't the code below return a rational number? > > X = BinomialDistribution[10, 6/10]; > F[x_] := CDF[X, x]; > Rationalize@F@4 > > Thankx. > > Bruce > I assume what you had in mind was: <<Statistics` X = BinomialDistribution[10, 6/10]; F[x_] := CDF[X, x] Rationalize[N[F[4]]] 0.166239 Note the N. Rationalize will only work on approximate numbers. The reason why it does not work above is because there is no rational number "sufficiently close", where the meaning of "sufficiently close" is relative to the size of the denominator of the fraction (the larger the denominator the closer the number has to be to the one we are approximating to be considered "sufficiently close"). If you just want any rational approximation, without caring about the size of the denominator, you can use: Rationalize[N[F[4]], 0] 75692233/455322801 Note that you got a pretty large denominator. If you would rather have a smaller one, you can get it but the approximation will be less accurate: Rationalize[N[F[4]], 10^(-6)] 194/1167 Andrzej Kozlowski

**References**:**Binomial Distribution***From:*Bruce Colletti <vze269bv@verizon.net>