Thread: probability of overweight OR female question

Hi, can anyone please help me with this question? I'm quite confused this moment.

In a certain population, containing an equal number of adult males and females, five percent are overweight. Twenty percent of the overweight are female. One person is selected at random from the population. What is the probability that the person is female OR overweight?

Should I try to calculate ? If that's what I should aim for, how do I do it? I'm so confused.

Originally Posted by tsang

Hi, can anyone please help me with this question? I'm quite confused this moment.

In a certain population, containing an equal number of adult males and females, five percent are overweight. Twenty percent of the overweight are female. One person is selected at random from the population. What is the probability that the person is female OR overweight?

Should I try to calculate ? If that's what I should aim for, how do I do it? I'm so confused.

.

From the given data you know that and you know that . From this you should be able to calculate and hence complete the calculation of .

If you need more help, please show all your work and say where you get stuck.

Originally Posted by mr fantastic

.

From the given data you know that and you know that . From this you should be able to calculate and hence complete the calculation of .

If you need more help, please show all your work and say where you get stuck.

Thanks a lot, I just couldn't work out how to approach before.
I just wonder about one thing please, how do I know it is P(O/F)=0.2, instead of P(F/O)=0.2? From the question wording, it feels like talking about give overweight is condition, then says the females for overweight is 0.2, so should that be P(F/O)=0.2?
Thanks a lot.

Originally Posted by tsang

Thanks a lot, I just couldn't work out how to approach before.
I just wonder about one thing please, how do I know it is P(O/F)=0.2, instead of P(F/O)=0.2? From the question wording, it feels like talking about give overweight is condition, then says the females for overweight is 0.2, so should that be P(F/O)=0.2?
Thanks a lot.

Quite right. My mistake. In which case you use Pr(F|O) = 0.2 and Pr(O) = 0.05 to get Pr(F and O).