Originally Posted by

**CaptainBlack** You have to make the assumption that being tall and wearing a blue shirt are uncorrelated. In this case that would mean that a tall person is as likely to be wearing a blue shirt as someone picked at random from the population in question. That is 10% of tall people are wearing blue shirts.

So that is 10% of 20% of the population are both tall and wearing blue shirts, so on **average** from your (random) sample of 100 people 20 are tall and 2 of those are wearing blue shirts.

In practice you will not always find exactly two tall blue shirt wearers but may find 0, 1, 2, 3, 4, ...

If you wish to pursue this further the number of tall blue shirt wearers in a random sample of 100 has a Binomial distribution b(n,100,0.02) (use Google/Wikipedia for more information).

CB