Find the probability of randomly selecting three science books and four history books from a box containing five science books and six history books.

Question

hba · Answer

5C3+6C4=

anonymous · Answer

@hba   Why would we be adding in this case?  It's not "three science books OR four history books"

hba · Answer

my bad :(

anonymous · Answer

No problem, I wasn't even sure that you were wrong, I was just confused.

anonymous · Answer

My guess is $\binom{5}{3} \times \binom{6}{4} \div \binom{11}{7}  $

It's assuming they meant to say "choosing 7 books randomly".  Because otherwise it could be 100% or even 0%.

hartnn · Answer

^ thats correct.

hba · Answer

The answer would be 5/11 then ?

anonymous · Answer

If I am correct then wolfram agrees: http://www.wolframalpha.com/input/?i=%285+choose+3%29+*+%286+choose+4%29++%2F+%2811+choose+7%29

hba · Answer

hmm,I am really sorry about the mistake i made :/