00:01
A landlord knows that there's a 10 % chance of not renting an apartment.
00:06
That tells me that to rent it the apartment, there is a 90 % chance of an apartment being rented.
00:13
For 16 to meet his monthly expenses, he needs 16 apartments rented.
00:19
So let's look at the following probabilities.
00:21
What is the probability that four are unrented? so this is going to be binomial.
00:26
And we don't know which four.
00:28
So how many apartments are there in this complex? there's 20 in the complex.
00:33
So we need to take a combination of 20 taking four at a time because we need to see which four are unrented.
00:40
And now unrented, that means that four of those 20 are not rented, which means the other 16 are rented.
00:54
So that's going to be the probability of exactly four being rented.
00:59
So now let's see.
01:00
The next one is going to be a little bit more lengthy.
01:04
The probability of 0 to 4 being unrented, which means we need the probability of 0, probability of 1, probability of 2, probability of 3, probability of 4, and then we get all of those and add it together.
01:20
Unrented.
01:21
So that means we've got to take a combination of 20, taking 0 at a time, 0 .10 to the 0 power, and then we have 0 .9 to the 20 power.
01:32
Makes sense.
01:33
All of them are rented.
01:35
Then we're going to have a combination of 20, taking one at a time.
01:39
We're going to have 0 .10 to the first power and 0 .9 to the 19th power.
01:45
19 are rented, one is not...