by kwame.appau Mon Jan 13, 2014 6:29 pm
-There are 6 ways of selecting 4 books of which 2 are novels.
-This is how to solve it.
-since the question ask for "selection" then it is combination problem.
-Therefore think of 4 slots and lets name the books (A,B,C,D,E,F) and the novels are "A" and "B"
-slots 1 and 2 for "A" and "B" and then slot 3 and 4 for (C,D,E,F)
-Since "A" and "B" are constant, there are 4 ways of selecting any of the remaining books for slot 3 and there are 3 ways of selecting any of the remaining books for slot 4. Hence 4*3/2!= 12/2!. The 2! is the number of ways of arranging books for slot 3 and 4.
-NOTE: order is not important so selecting (A,B,C,D) is the same as selecting (A,B,D,C).
- Hope that helps!