You know how to do it. You just don't know what it is they want you
to do, because they're speaking in foreign tongues.
"Mean" is just another word for "average".
"Population mean" is just "the average of the bunch".
They're asking for the average length of the ten movies.
Do you remember how to find the average ?
It's (the sum total of all the items) / (the number of items in the bunch).
