lazyashell wrote:
There are 4 fiction books and 6 non-fiction books in a reading list. 3 of the non-fiction are biographies. Each person is required to select 3 books from the list. What is the probability that at least one fiction book, and at most one biography are selected?
Give your answer as a fraction.
There are several ways to solve this question. I will try to explain it in simple terms:
We have 4 cases to analyze:
1) The probability of picking only fiction books.
2) The probability of picking at least a fiction book and a biography.
3) The probability of picking at least a fiction book and non-biography books.
4) The probability of picking a fiction book, a biography book, and a non-biography book.
With those cases we have covered all the possibilities. Lets calculate them:
1) The probability of picking only fiction books.4103928=1302) The probability of picking at least a fiction book and a biography.We have 3 combinations in this case (
B stands for Biography, and
F for fiction):
B,F,FF,B,FF,F,B(4103938)∗3=3203) The probability of picking at least a fiction book and non-byography books.We have 6 cases (
Nb stands for non-biography):
Nb,F,FF,Nb,FF,F,Nbwhose probability could be written as:
(4103938)∗3=320and also, we have:
Nb,Nb,FNb,F,NbF,Nb,Nbwhose probability could be written as:
(3102948)∗3=1104) The probability of picking a fiction book, a biography book, and a non-biography book.In this case, we have 6 combinations (
3! because we have 3 different items that have to be mixed):
F,Nb,BF,B,NbNb,F,BB,Nb,FB,F,NbNb,B,Fand the probability is:
(4103938)∗6=620Now, we have to sum each probability in order to consider all the cases:
130+320+330+110+620=4460=1115