00:01
In this question, you will use the idea of permutation to find the number of ways to arrange the scrolls.
00:12
You need to find the number of ways to line up the 15 different objects.
00:20
Since the question requires that the scrolls must alternate elemental type, we must start the line up with a windstance, spell because if we start a line up with a strength spell, there won't be enough strength spells for us to alternate elemental type every time.
00:46
In other words, you'll be forced to arrange two wind spells close next to each other at the end.
00:55
So we start the line up with a wind spell.
00:59
To make it clear, we'll use a square to represent a wind spell position and a circle to represent a strength spell position.
01:34
We start with a wind spell scroll, then followed by a strength spell, then alternate, then alternate, and so on, so forth.
01:52
There are total 15 scrolls.
02:09
1, 2, 3, 4, 5, 6, 7...