Compute like you read: left to right.

Paper addition goes right to left with carries. In your head, go left to right: big parts first, then refine. For 47 + 36, do 47 + 30 = 77, then 77 + 6 = 83. The partial answer is always close to the real one, so you can start typing the leading digit sooner — and there’s nothing to “carry.”

Know every pair that makes 10 (7+3, 6+4…) and the 100-complement of any 2-digit number instantly (37 → 63). Subtraction becomes a complement lookup: 132 − 87 is “87 needs 13 to reach 100, plus 32” = 45. Complements also spot friendly regroupings in sums: 38 + 25 + 62 → (38 + 62) + 25 = 125.

Distribute over friendly numbers: 17 × 6 = (10 + 7) × 6 = 60 + 42 = 102. Multiply by 5 as “×10, halve”: 18 × 5 = 90. By 9 as “×10, minus one copy”: 14 × 9 = 140 − 14 = 126. Near-squares use (n−1)(n+1) = n² − 1: 12 × 12 = 144, so 11 × 13 = 143.

Mid-sprint prompts like 3 + 4 × 6 are precedence traps — multiplication first, always (answer 27, not 42). Scan the whole prompt before computing: find the × and ÷, resolve them, then add. For sequences, check the differences first (constant → arithmetic), then ratios, then growing differences.

A wrong answer keeps you stuck on the same puzzle — an error costs the miss plus a full re-solve. On tiers 1–3, speed wins; from the sequences and percentages onward, a half-second sanity check (right digit count? plausible magnitude?) is cheaper than a retry. Percentages divide cleanly here: 25% = quarter, 75% = three quarters, 15% = 10% + half of that.