00:01
For problem 40, we are working to arrange five different math books.
00:06
The only exception is two of them are algebra books, which must be paired together.
00:11
So we can think of this as there's geometry book, algebra one, algebra two, calculus, and trigonometry.
00:20
And so these are our five books.
00:22
However, really, these are a pair.
00:25
And as such, they will act as essentially one book.
00:28
So, for the first spot, there are one, two, three, four options, so four options...