00:01
Let's rearrange the letters in the word number and figure out how many different ways this can be done.
00:06
But we have the condition where e and r must remain next to each other.
00:09
They can switch orders, so r -e is perfectly acceptable, but they still have to be next to each other.
00:15
So how many different ways can this be done? let's consider bonding this er together into one letter, which i'll just represent with this triangle.
00:25
So that means we have essentially five letters.
00:30
M, b, and triangle.
00:32
So how many different ways can we order these? well, there's five different spots in our new word.
00:39
And so for the first letter, there's five different possibilities, then four for the next, three, two, one...