In a stacked-triangle pattern, the number of small triangles in the base row of shape 1, 2, 3, ... follows 1, 3, 5, 7, .... How many small triangles are in the base row of the 10th shape?
- A.17
- B.18
- C.19 ✓
- D.21
Explanation: The base-row count follows 2n−1. For the 10th shape: 2×10−1 = 19.
Class 6 IMO Mathematics Olympiad practice · Algebraic Thinking · Patterns in Mathematics
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