What This Drill Trains
The Grand Challenge mixes skills from earlier phases into one longer marathon. It is less about learning a brand-new trick and more about flexible retrieval: recognizing which tool fits the problem in front of you. Treat it like a recital after practice — useful once foundations, percentages, and advanced shortcuts already feel familiar.
How to Think During the Round
Spend half a second classifying the problem before calculating: Is it a table fact? A round-and-adjust candidate? A percentage anchor? A two-step chain? Classification prevents using a heavy method on a light problem. When stuck, fall back to decomposition rather than freezing on a forgotten trick.
You have 120 seconds. Accuracy still outranks raw speed: one calm method repeated well beats a streak of guesses. After the timer ends, notice which problems felt sticky — that short review is where real improvement happens.
Worked Examples
Study these before you press Start. Try to recreate the thinking without looking at the answer first.
15% of 200
Thinking: 10% of 200 is 20; 5% is 10; total 30. Compose anchors instead of inventing a new rule.
Answer: 30
43 × 11
Thinking: Split-and-add: 4, 4+3=7, 3 → 473. Do not grind long multiplication for ×11.
Answer: 473
199 + 68
Thinking: 200 + 68 = 268; subtract the extra 1 → 267. Compensation beats digit-by-digit here.
Answer: 267
Common Mistakes
- Forcing an advanced trick onto a problem that only needs a basic fact.
- Panicking when the mix changes and abandoning accuracy for random speed.
- Skipping warm-up on weak topics, then blaming the marathon format.
Practice Tips
- Only attempt Grand Challenge after comfortable scores on earlier phase drills.
- After each marathon, list the problem types you missed and revisit those stage lessons.
- Two focused 60-second drills beat five exhausted marathons the same day.
Suggested Session Plan
- Read the method section once if this skill is new.
- Cover the answers and re-solve the three worked examples aloud.
- Start the timed round and stick to one strategy.
- Replay once, then write down any fact or pattern you missed.
Prefer a structured curriculum instead of random drills? Browse all learning stages or read the complete mental arithmetic guide . More timed drills live on the games hub.