Upper and lower bounds in rounding to 1 Decimal place I have a measurement $a=8.3$cm to 1 d.p. I'd like to find the upper bound of this. Why is the upper bound $8.35$cm? not $8.3\dot{4}$cm? Surely 8.35 rounds to 8.4cm?
And the lower bound $8.25$cm not $8.24\dot{9}$cm?
The upper bound is 8.35 cm because anything less than 8.35 will round to 8.3, but anything 8.35 or greater will round to 8.4. 8.35 itself does not round to 8.3, but it is the smallest such number, or the least upper bound.

Similarly, the lower bound is 8.25 because anything less than 8.25 rounds to 8.2, and 8.25 rounds to 8.3, so 8.25 is the lower bound (And also the minimum).

Also, your question about $8.25$ and $8.24\dot9$ doesn't really make much sense -- those two decimals represent the same real number.
Its because the upper bounds of 8.3 is 8.349999999999.... So you round it up to 2 decimal places which is 8.35.