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December 22nd, 2018, 10:29 AM   #1
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Probability and statistics

If 3 books are selected at random from a shelf containing 5 Novels, 3 Books of poems and a dictionary, what is the probability that

a) dictionary is not selected
b) 2 Novels and 1 Book of poems are selected

I tried doing it, however I am unable to guess what will go in the denominator part of the answer. Can someone please help me solve this question?
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December 22nd, 2018, 10:47 AM   #2
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of the 9 books only 1 is a dictionary

so P[not selecting dictionary] = 8/9

there are 5 novels from the 9, we select one, now there are 4 novels of 8
and we select another one, now there are 3 poems of 7, and we select one.

P[2 novels and 1 poems] = 5/9 4/8 3/7 = 60/504
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December 23rd, 2018, 11:40 AM   #3
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Quote:
Originally Posted by romsek View Post
there are 5 novels from the 9, we select one,
now there are 4 novels of 8 and we select another one,
now there are 3 poems of 7, and we select one.

P[2 novels and 1 poems] = 5/9 4/8 3/7 = 60/504
...and the order doesn't matter; like:
3 poems from the 9: 3/9
4 novels from the 8: 4/8
5 novels from the 7: 5/7

3/9 * 4/8 * 5/7 = 60/504 = 5/52

Thanks Romsek: yo my probability teacher!!
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