This is like a common core math problem. Poorly worded to the point of obscuring any real math talent that could be applied in finding a “correct” result, and instead we get to debate what the question means.

A more interesting question, I think, is given a POW algorithm which adjusts difficultly to target a 10 minute block rate, and assuming network hash rate is constant and propagation is instant, what percentage of blocks take 20 minutes to solve? 60 minutes? And what’s the odds of solving two blocks in <= 60 seconds?