alleryHow many entries does a 9 × 9 chart need if a × b = b × a is used and a ≥ b?
A54
B81
C36
D45
Answer & Solution
Correct answer: D. 45
1. The 1 to 9 grid has 81 entries.
2. Because a × b = b × a, entries with a ≥ b are enough.
3. That leaves 45 (9 × 10 / 2).
_Source: Wikipedia, Multiplication table (CC BY-SA 4.0, rev 1379867676), Modern times_
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