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This is a fairly simple math problem from a programming challenge but I'm having trouble wrapping my head around it. What follows is a paraphrase of the problem:
Kundu has a Bubble Wrap and like all of us she likes popping it. The Bubble wrap has dimensions NxM, i.e. it has N rows and each row has M cells which has a bubble. Initially all bubbles in filled with air and can be popped. What Kundu does is randomly picks one cell and tries to pop it, there might be a case that the bubble Kundu selected is already popped. In that case he has to ignore this. Both of these steps take 1 second of time. Tell the total expected number of seconds in which Kundu would be able to pop them all.
So I know that the expected value is the sum of the product of the random variable x and the probability of that instance of x occurring but I'm having trouble parameterising the problem statement. What's the x and how does time play into it?