A number machine changes 4 to 13, 7 to 22, and 10 to 31. Which rule is used?
- A.×2 + 5
- B.×3 + 1 ✓
- C.×3 − 1
- D.×4 − 3
Explanation: 4×3+1=13, 7×3+1=22, 10×3+1=31 — all match ×3+1.
Class 6 IMO Mathematics Olympiad practice · Patterns & Sequences · Number & Letter Sequences
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