ah this is one of those clever interview questions. well i'm pretty good at math so this should be no problem.
first we need to know how many people there are. that's like seven billion now.
next we need to know how many basketballs there are per person. i happen to know that i, a representative sample, own zero basketballs. so that's a reasonable guess
now we simply multiply, and we can conclude that there are approximately zero basketballs in the world. of course this is to one significant figure, so the true answer could be as high as nine