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Explanation:
The upper boundary, or upper bound, is a fence of sorts.
Note how the following values all round to 34.9, when rounding to one decimal place
We can keep going with the pattern of 9s at the end and whatever value you form will still round to 34.9; so you can see that there is no largest value we can reach that will round to 34.9
All of those values are slowly approaching 34.95, which is the upper fence I mentioned. We can get closer and closer to this value, but we can't actually reach it. Otherwise, 34.95 will round to 35.0
