Probability is Killing me

[solstice]

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?
Answer: 10

2. How many different ways can two books be chosen from 10 books, if two particular books are to never be chosen?
Answer:28

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.

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[athlete19]

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]

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]

Thanks for your help guys.

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]

Is she hot? I def gotta check that out!

 

[solstice]

Is she hot? I def gotta check that out!

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