SOLUTION: there are k different books and i copies of each in a library. the number of ways in which a student can make selection of one or more book is

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Question 823952: there are k different books and i copies of each in a library. the number of ways in which a student can make selection of one or more book is
Answer by Edwin McCravy(20060) About Me  (Show Source):
You can put this solution on YOUR website!
there are k different book titles and i copies of each title.
for each of the k titles we can answer this pair of questions:

A. Will I select a book with this title?
B. Will I NOT select a book of this title?

in two ways, either YES or NO.

The number of ways in which a student can make a selection of one or
more books is 2×2×2×···×2 where there are k 2's all multiplied together.
So there are 2k ways to select k titles. Suppose the copies of each
title are numbered 1 through i.  The for each of those 2k ways to
select a title, there are i ways to select a copy number.  So the answer is
the number of ways in which a student can make selection of one or more books is
2k*i - 1
Why the -1?  Because we must subtract the number of ways he answers "no" to
question B all k times, which is 1 way.  If he answers "no" to them all, he
walks out of the library empty-handed. If you want to count that case as
an "empty selection", then it's: 

2k*i

without the -1.    

Edwin