Blood testing for disease in groups

[alThor]

Did you try the question yourself first? If there is an exam in this class, you'll not benefit from just reading the answer on a forum. You have to learn the thought process that goes with it.

A good hint, though, would be to suggest that you first answer the question as if there were only 10 people instead of 100. Get the EV and Var for that case. Then, realize that the 100 people are 10 independent groups of 10. Now apply what you were probably taught about EV and Variance of sums.

alThor