00:01
So in this question we're given the set of letters l -g -b -t -q -i -a.
00:14
So how many ways are there to form a string containing exactly one copy of each letter? well, this is going to be the number of permutations of the set.
00:26
So let's call this set s.
00:29
So this is going to be the size of s factorial.
00:33
So this is 7 factorial.
00:38
So 7 factorial is 5 ,040.
00:44
So now part b, suppose all license plates in a certain state consists of three distinct consonants followed by two distinct vowels.
00:52
How many such license plates are there? well, the number of license plates is going to be the number of ways of picking three consonants times the number of ways of picking two vowels.
01:10
And there are four, well, there are five consonants for us to choose from.
01:13
So this is 5 choose 3.
01:16
And there are two vowels for us to choose from.
01:23
But then we've got this 5 choose 3, but then all the different permutations of that are also going to be a different number plate.
01:32
So we've got a 3 factorial.
01:34
And then we've got to pick two vowels...