Instead of LBs, I want Bux

As title mentions, I have already completed my LBs, so now I’m focused on the Bux collection.

I don’t understand the percentage thingy part of the ice cream event though.

Also, do I buy in bulk or one by one, if the rewards are all random based on the percentages, should I buy one by one I hopes that some will be Bux; or I can buy in bulk and risk thatthe entire thing is either Bux or not.