Discussion
A person has 2 parents, 4 grandparents, 8 great-grandparents, and so on. Find the number of his ancestors during the ten generations preceding his own.
Answer: B
The ancestors form a geometric progression with \( a = 2 \), \( r = 2 \).
\[ S_{10} = \frac{2(2^{10} - 1)}{2 - 1} = 2(1024 - 1) \]
\[ = 2046 \]
2048 is \( 2^{11} \), two more than the sum - the nearest trap.
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