I like to do a little exercise when I give a talk (like the one above), which is to ask the room how many golf balls fit in a bath tub.
Not because I care about the answer, but because it's interesting to watch the way people answer the question.
It's interesting to see how few people just Google the answer. Because if they did, it's likely they'd find this page. For some reason, people think they have to figure the answer out on their own, with no help. I think it's a function of how we're taught in school that we have know know things. But I believe it's actually more important to know how to know things.
The answer is: It depends on the size of the bathtub. It also depends on the size of the golf balls. And whether or not the bathtub is empty or full. And all sorts of other assumptions.
This is why it's so interesting to see people answer the question, because they make a lot of implicit assumptions – including (usually) assuming they have to figure the answer out themselves, instead of just searching for the answer.
That's why the question is really about thinking outside the box.
For the record, if you assume an empty, standard sized bathtub (about 60" long and 32" wide x 18" tall, that's 34,560 cubic inches) and a standard sized golf ball of 2.5 cubic inches (4/3 * pi * .85), you could fit 13,824 golf balls. However, due to the sphere packing problem (lots of empty space between the balls, even when stacked) you have to multiply that answer by 0.74, which gives you 10,229.76 golf balls. We'll just round up to 10,231 when you account for that extra golf ball in the drain!