00:01
Okay, part a.
00:02
I want five characters and i can use any of these characters here.
00:09
And there are nine in total, which means i have nine choices for the first location.
00:16
Five numbers, four letters.
00:20
Then i can't repeat, so eight left to go here, then seven, then six, then five.
00:26
So my answer will be that times together.
00:30
So nine times eight times seven, six times five, 15 ,120 possible passwords.
00:47
Okay, part b.
00:48
What i want are two letters followed by three numbers.
00:54
So letters can be a, b, c, or d.
00:58
So what i have then are four choices here and then three choices left.
01:04
The numbers, any of these five.
01:07
So i can have five choices here, then four choices here and three choices here.
01:15
And that times together gives the answer.
01:18
So four times three, 12 times 20 times three, answer 720 different passwords.
01:33
Okay, the last one.
01:34
I want two letters and three numbers, but any order.
01:39
So you could have then number, number, number, letter, letter.
01:48
That's three numbers and two letters.
01:53
And could be n, n, l, n, l, could be l, l, n, n, n.
02:04
I want to work out first number of different ways of arranging three numbers and two letters...