Need help on Probablility problem

  • Thread starter Thread starter ReAL
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ReAL

I have a problem for class i cant figure out how to do this is it:

I have to create a worksheet that displays the percentage of peopl
having the same birthday and the percentage of them having differen
birthdays. My problem is i have no idea what formula to use to ge
these percentages for each amount of people. If anyone can help i
would be greatly appreciated
 
This is not really the right forum for this question - you should come
here with the formula and ask how to make it work in Excel.

You're in luck, I work with statistics and probability every day, I
think this might be what you need:

For one person, there are 365 distinct birthdays.

For two people, there are 364 different ways that the second could
have a birthday without matching the first.

If there is no match after two people, the third person has 363
different birthdays that do not match the other two. So, the
probability of a match is 1 - (365)(364)(363)/(365)(365)(365).

This leads to the following formula for calculating the probability of
a match with N birthdays is:

1 - (365)(364)(363)...(365 - (N - 1))/(365)^N.

Now, how are you supposed to calculate this in Excel? Does your
instructor want to see a filled series of formulas? A macro? A chart?
Histograms?

Is this an Excel class or a statistics class?

The Disclaimer: This may not be even close to how your instructor
wants you to do it.

The Advice: Pay more attention in class. :-)




I have a problem for class i cant figure out how to do this is it:

I have to create a worksheet that displays the percentage of people
having the same birthday and the percentage of them having different
birthdays. My problem is i have no idea what formula to use to get
these percentages for each amount of people. If anyone can help it
would be greatly appreciated.


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Mike Argy
Custom Office Solutions
and Windows/UNIX applications

Please post on-topic responses to the newsgroup

To e-mail me, remove nospam from the address in the headers
 
Its an Excel class, and i just need a spreadsheet with two columns with
the percent of same birthday and percent of different birthday. I have
to print one out with the formula to get these percents and one with
the percents themselevs.

Is 1 - (365)(364)(363)...(365 - (N - 1))/(365)^N the formula i need to
put into excel to get what im looking for?
 
do you have a column of Birthday's and you actually want to count how many
birthdays are unique and how many match.

assume the birthdays are stored as dates in A1:A50

use a helper column

for example in B1 put in a formula

=if(Countif($A$1:$A$50,A1)>1,"Dup","Unique")

then drag fill down the column to B50

you can then use
=Countif(B1:B50,"Unique")/50

=Countif(B1:B50,"Dup")/50

and format the cells with the formulas a percent.

--
Regards,
Tom Ogilvy


ReAL said:
Its an Excel class, and i just need a spreadsheet with two columns with
the percent of same birthday and percent of different birthday. I have
to print one out with the formula to get these percents and one with
the percents themselevs.

Is 1 - (365)(364)(363)...(365 - (N - 1))/(365)^N the formula i need to
put into excel to get what im looking for?


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