The most important thing about these types of problems is understanding what is being asked, and figuring out certain "code words". In your problem for example they tell you that of a birds day, 10% of it is spent doing some activity. Which means 90% is spent doing something else. If we were to take the sample space of All Blue Bird Activity, it would be composed of two parts: one part milling about at some bird feeder and one part doing something else.

Secondly, they are asking what behavior you can expect to see. Well, expectation (as you should know) is just another way of saying "average": On average, how many minutes should three birds spend at her bird feeder?

And thirdly, you should recognize, that the fact that one bird has gone to this persons bird feeder, probably isn't going to affect another bird going in. So if we call X1, X2 and X3 independent events, where X is the number of minutes bird N is spending at this bird feeder, then we can go about figuring out the problem which is simple E[# of minutes of three birds] = X1+X2+X3.

Therefore, over a 12 hour period (or 720 minutes), one blue bird should spend 72 minutes at her bird feeder. How many minutes should three spend?