When you are rounding off with hole numbers it doesn't matter if it is with tens or hunderds the principle stays the same.
When you are rounding off with tens only the last 2 numbers are effected so with 21974 it's only about '74'.
With tens if the last number is a 5 or above it gets rounded up so 15 becomes 20. If the number is a 4 or lower it gets rounden down so 74 becomes 70.
Rounding up with hunderds is almost the same but not its about the last 3 numers in 21974. The rounding off rules stay the same but then with a zero behind it 150 becomes 200. This doesnt mean that 974 becomes 740 the rules stay the same but the numbers may change so 974 becomes 1000.
