863 — add 500, then subtract 11.

374 + 489 → 374 + 500 = 874 → 874 − 11 = 863.

This is a useful variant of compensation: rounding by 11 is still easy if the round number makes the main addition trivial.

62 = 50 + 12, so the first part is 25 + 12 = 37 and the tail is 12² = 144 — which overflows and carries.

• First part: 25 + 12 = 37.
• Tail: 12² = 144 → two-digit slot holds 44, carry the 1.
• Combine: 37 + 1 = 38, then 44 → 3844.

Check: 62² = 3844. ✓ Whenever the deviation d is large enough that d² ≥ 100, the hundreds digit of d² carries into the first part — the same overflow rule as the near-100 multiply.