What are the largest and the smallest round to 400000 by ten thousand?
Assuming you are dealing with whole numbers only:
Half of the numbers round up and half round down.
Half of ten thousand is five thousand.
Therefore 400000 ± 5000 round to 400000 to the nearest 10000;
except that numbers exactly half way round up, so the maximum is
one less than this.
→ smallest to round [up] to 400000 is 400000 - 5000 = 395000
→ largest to round [down] to 400000 is 400000 + 5000 - 1 =
404999