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Probability question

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by jfranco23 » Fri Mar 13, 2009 4:57 pm
There are 8 books on a shelf, of which 2 are paperbacks and 6 are hardbacks. How many possible selections of 4 books from this shelf include at least one paperback?

A. 40
B. 45
C. 50
D. 55
E. 60
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by cramya » Fri Mar 13, 2009 5:01 pm
Atleast 1 paper back could be 1 paper back or 2 paperbacks


1PAPERBACK 3 HARDBACKS + 2 PAPERBACKS 2HARDBACKS

2C1*6C3 + 2C2*6C2

= 55
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Re: Probability question

by sureshbala » Fri Mar 13, 2009 8:39 pm
jfranco23 wrote:There are 8 books on a shelf, of which 2 are paperbacks and 6 are hardbacks. How many possible selections of 4 books from this shelf include at least one paperback?

A. 40
B. 45
C. 50
D. 55
E. 60
Total number of selections = 8C4 = 70

Number of ways on choosing all hardback copies( i.e no parperback) = 6C4= 15.

Hence number of ways of selecting at least one paperback = 70-15 = 55
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