The Museum of HP Calculators

HP Forum Archive 19

 HP20b's 1-variable weighted functionMessage #1 Posted by Ric Lombardo on 25 Apr 2010, 6:34 a.m. Has anyone had a go at trying to implement the 1-variable weighted function that is part of the Statistical Suite available on the HP20b. Apart from a brief cursory mention in HP's official manual for this calculator there is no example or explanation of what this function does or how to implement it. I presume it helps one to determine the expected value of a random variable by inputting random variable outcomes into the X: register and their associated probabilities in the Y: register but I cannot seem to get any results. If anyone knows how this function operates I would appreciate some assistance or guidance. Cheers and have a nice day, Ric

 Re: HP20b's 1-variable weighted functionMessage #2 Posted by Walter B on 25 Apr 2010, 6:47 a.m.,in response to message #1 by Ric Lombardo AFAIK the 20b calculates a *weighted mean*. It does it the conventional way with the weights in y. I don't remember any "weighted function" but I don't have my calc at hand.

 Re: HP20b's 1-variable weighted functionMessage #3 Posted by Gene Wright on 25 Apr 2010, 7:56 a.m.,in response to message #2 by Walter B This is for the 30b, but take a look here:

 Re: HP20b's 1-variable weighted functionMessage #4 Posted by Ric Lombardo on 26 Apr 2010, 7:19 a.m.,in response to message #3 by Gene Wright Thanks guys for your help. I see now that the trick is that the Y-values are entered as frequencies {F} and NOT as relative frequencies {Fi/Sum(Fi)} (or probabilities) which is what I thought I had to do. In essence then this is not very much different from the approach used with the HP 10B and HP10BII. By the way Gene I think that little Guide entitled: "The HP 20b Business Consultant" was really great and that in your next update you might want to slip in a line or two on the matter discussed here. Thanks again for you time and assistance, Ric

 Re: HP20b's 1-variable weighted functionMessage #5 Posted by Gene Wright on 26 Apr 2010, 8:07 a.m.,in response to message #4 by Ric Lombardo Oh, I did not write that. Tough to cover everything that is important in a small guide, however. :-)

 Re: HP20b's 1-variable weighted functionMessage #6 Posted by Ric Lombardo on 30 Apr 2010, 10:50 a.m.,in response to message #5 by Gene Wright Interestingly, even though the HP20b was designed to replace the simpler but very popular HP-10B and HP-10B2, the latter two calculators can provide a weighted mean irrespective of whether the weights are entered as frequencies or relative frequencies. Its a pity the HP-20B dispenses with this flexibility as it means one cannot compute the expected value E(X) of a random variable X in the conventional fashion.

 Re: HP20b's 1-variable weighted functionMessage #7 Posted by Gene Wright on 30 Apr 2010, 11:09 a.m.,in response to message #6 by Ric Lombardo True, but the frequency statistics have a much greater breadth to them than the basic "weighted average". To get a weighted average is actually pretty easy and requires rethinking the input only slightly. If you have a random variable with a 40% chance of 10 and a 60% chance of 5, you can of course input the weights as 40 and 60 in 1 Freq mode or even as 4 and 6 in 1 Freq mode and the Descriptive submenu reports the correct mean.

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