Find the sum of the G.P.:
8/7, 8/49, 8/343, 8/2401, … to n terms.

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UP Police SI (दरोगा) Official PYP (Held On: 27 Nov 2021 Shift 1)
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  1. 6/7(1 - (1/7)ⁿ)
  2. (1 - (1/7)ⁿ)
  3. 5/7(1 - (1/7)ⁿ)
  4. 4/3(1 - (1/7)ⁿ)

Answer (Detailed Solution Below)

Option 4 : 4/3(1 - (1/7)ⁿ)
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Detailed Solution

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Given:

The G.P. series is: 8/7, 8/49, 8/343, 8/2401, … to n terms

First term (a) = 8/7

Common ratio (r) = 1/7

Number of terms (n) = n

Formula used:

Sum of G.P. to n terms: Sn = a × (1 - rn) / (1 - r)

Calculations:

Sn = (8/7) × (1 - (1/7)n) / (1 - 1/7)

⇒ Sn = (8/7) × (1 - (1/7)n) / (6/7)

⇒ Sn = (8/7) × (7/6) × (1 - (1/7)n)

⇒ Sn = 8/6 × (1 - (1/7)n)

⇒ Sn = 4/3 × (1 - (1/7)n)

∴ The correct answer is option (4).

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