3.498546 to 3 decimal places
on a number line would lie between 3.498 & 3.499
The midpoint between these two numbers is 3.4985
3.498546 is closer to 3.499 - only just over halfway (by 0.000046)
so correct (or rounded) to three decimal places it is 3.499
This one is relatively straightfoward numbers such as 4.99546 (correct to 2 decimal places) tend to cause more issues about whether to write 5.00 or just 5
Rounding a decimal number to a given number of places is given easier than to the nearest ten thousand etc as pupils do not need to fully appreciate place value of each digit within the given number as they simply count the figures after the given decimal point