Question:

If \(2^{10}+2^{9}\cdot 3^{1}+2^{8}\cdot 3^{2}+\ldots+2\cdot 3^{9}+3^{10}=S-2^{11}\), then \(S\) is equal to :

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The left side is a GP with first term \(2^{10}\), ratio \(3/2\) and 11 terms (or use \(a^{n+1}-b^{n+1}\) over \(a-b\)).
Updated On: Nov 5, 2026
  • \(\frac{3^{11}}{2}+2^{10}\)
  • \(3^{11}-2^{12}\)
  • \(2\cdot 3^{11}\)
  • \(3^{11}\)
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The Correct Option is D

Solution and Explanation

The sum has 11 terms: \(\sum_{k=0}^{10}2^{10-k}3^{k}\), a GP with first term \(2^{10}\) and common ratio \(\frac{3}{2}\).
Sum \(=2^{10}\cdot\frac{(3/2)^{11}-1}{(3/2)-1}=2^{10}\cdot 2\left(\frac{3^{11}}{2^{11}}-1\right)=3^{11}-2^{11}\).
So \(3^{11}-2^{11}=S-2^{11}\), giving \(S=3^{11}\).
Answer: (4) \(3^{11}\)
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