The rule to round p decimal numbers is as follows.
If the number that you are rounding up is followed by a number between 0 and 4, then you leave it as it is, i.e. round it to the nearest ten.
For example
8.52 the second decimal is between 0 and 4, then you can round it as 8.5
If the number that you are rounding is followed by a number between 5 and 9, then you have to round it to the following ten.
For example
8.56 the second decimal is greater than 5 so the rounded value is 8.6
For the given value, the second decimal value is zero, so you have to leave the first decimal value without change:
17.501 → 17.5
