Question 1162812
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A)...<br>
3C2 = 3 ways to choose the two history books that are to be together as a unit
2P1 = 2 ways to order those two history books
3C2 = 3 ways to choose the two math books that are to be together as a unit
2P1 = 2 ways to order those two math books
4P4 = 24 ways to order the four units (pair of history books, pair of math books, single history book, and single math book)<br>
ANSWER: 3*2*3*2*24 = 864<br>
B)...<br>
Grammatically, this makes no sense with the given numbers of books.<br>
"... and vice versa" means there are two math books following two history books, and two history books following two math books.  That would mean there have to be four history books... but there are only three.<br>