Use rounding-and-adjusting to compute 823 − 398.

Subtract a round number, then correct — but for subtraction the correction goes the opposite way.

823 − 398 → subtract 400: 823 − 400 = 423 → you took away 2 too many, so add 2 back → 425.

Check: 823 − 398 = 425. ✓

Watch the direction: when you round the amount you're subtracting up, you removed too much, so you add the difference back. (In addition, over-rounding means you subtract.) Getting this sign wrong is the classic compensation error.