1. binomial random variable

Each of 1000 people in a place independently has a certain
disease with probability 0.005.

i Find the probability that at least one person has the disease
ii. Find the probability that there is more than one person has the disease, if we know that there is at least one person having the disease
iii. If one of the 1000 people knows that he has the disease. What does
the probability that more than one person (including himself) has the
disease

For example first question is it 1-(1-0.005)=0.995??????

2. Originally Posted by someone21
Each of 1000 people in a place independently has a certain
disease with probability 0.005.

i Find the probability that at least one person has the disease

Mr F says: 1 - Pr(X = 0) = ....

ii. Find the probability that there is more than one person has the disease, if we know that there is at least one person having the disease

Mr F says: Use the conditional probablity formula on ${\color{red}Pr(X > 1 | X \geq 1)}$.

iii. If one of the 1000 people knows that he has the disease. What does
the probability that more than one person (including himself) has the
disease

For example first question is it 1-(1-0.005)=0.995??????
Let X be the the random variable number of people who have the disease.

And do we use binomial probability here??

4. Originally Posted by someone21

And do we use binomial probability here??
I can't see the difference between ii and iii ......

how to you still solve (ii) or(iii)

I don't understand how to do calculation

6. Originally Posted by someone21
Calculate $Pr(X > 1 | X \geq 1)$ using the usual conditional probability formula.