Hi there.
To start, we have to understand where the ten the place is.
Hint: it's 1 place behind the decimal point.
Now we need to know what numbers behind the tenths place make it round up or down.
If the number behind it is 4 or under, round down.
5 & up, round up.
In this case, 830.248 has 2 numbers behind the decimal, so we have to round those THEN the 2 in the tenths place.
830.25 to 830.3
Your answer is D. 830.3
I know this was lengthy, sorry. Just wanted to explain :p