I don't get it.
Certainly I agree with what Alan has said. The question tells you to work it out like as if there is no hole. That is fine. BUT
Isn't this bead just a sphere with a hole in it? If you put a hole through the middle of the bead then the volume if the bead has to decrease. Certainly if the diameter of the hole is 0 then there really is no hole and the volume is as it was to start with. But if the diamer of the whole is equal to the diameter of the bead then there is no bead left and the volume of the bead is 0. I obviously do not understand the wording of this problem. 
I think the penny just fell! The volume is the constant, the radius is the variable, now I've got it!!
The answer was obvious from the wording, but I haven't even thought about why that would be so yet. - But finally I think I understand the problem!
I do not know what level you are studying at nosomathpro but the answer is given in the question. You do not even have to understand the question to get the answer (I did not). Is this question just trying to teach you to pull out the relevant details and ignore the rest? Not a difficult problem, just a word exercise??
WOW - I am going to be thinking about this for days. Thanks for sharing it with me notsomathpro and thank you Bertie for drawing my attention to this question. Otherwise i probably would not have even thought about it at all. 
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Everything i have written is real but I have also demonstrated how a question asker can 'discussed' their question.