# Probability is Killing me

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#### solstice

##### Full Member
5+ Year Member

Can some one explain these two questions from CDm, please?

1. Three men and two women are candidates for two vacancies. A selector can choose two candidates. In how many ways can he make his selection?

2. How many different ways can two books be chosen from 10 books, if two particular books are to never be chosen?

And one general question: Is there any good resourse for learning probability. To me seeing one question here and there with solution does not work. I need solid source to study from. Any advise is appreciated.

#### athlete19

##### Full Member
7+ Year Member
Same strategy for both problems... this is actually a pretty common question on the math section i've come to notice.

so for the first one... 10 books, 2 never chosen, so ur only selecting from 8 possible books. so when you choose your first book, there are 8 possibilities, when u choose the second book there are 7 possibilities.... 8x7=56. so there are 56 possibilities but half of them are recycled since your choosing 2 books so u may have AB and BA. so divide the 56 possibilities by 2 and you get your answer, 28.

same strategy for the second.... there are 5 candidates total (3 + 2). you want to choose 2. so for your first choice, there are 5 possibilities, then your second choice, you have 4 remaining possibilities. 5 x 4 = 20. once again, since your choosing 2, you are gonna have half of them recycled. therefore, 20/2 = 10 (the answer).

if you were choosing three, you would just divide by 3, etc.

#### jorasic

##### Full Member
Both are combination problems, review that along with permuations

For both just plug it in:

a C b = a! / (b!*(a-b!))

For the first Question.. 5 C 2 = 5!/ (2!*3!)

Same for the second.

#### solstice

##### Full Member
5+ Year Member

I totally freeze when I see probability like Ted in Scrubs when he sees the mal practice attorney girl (just to give you some perception).

#### jorasic

##### Full Member
Is she hot? I def gotta check that out!

#### solstice

##### Full Member
5+ Year Member
Is she hot? I def gotta check that out!

haha. I have yet to see a girl who is not hot in that show.