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प्रश्न
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.
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उत्तर
Here, the ancestors of the person form the G.P. 2, 4, 8, 16, ........
Now, first term, a = 2
And, r = 2
∴ Number of his ancestors during the ten generations preceding his own,
\[S_{10} = 2\left( \frac{2^{10} - 1}{2 - 1} \right) = 2 \left( 1024 - 1 \right) = 2046\]
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