Find the sum of the G.P.: 

4/74/494/3434/2401... to n terms.

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UP Police SI (दरोगा) Official PYP (Held On: 21 Nov 2021 Shift 1)
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  1. 2/3(1-(1/7n))
  2. 5/4(1-(1/7n))
  3. 5/7(1-(1/7n)) 
  4. 2/7(1-(1/7n)) 

Answer (Detailed Solution Below)

Option 1 : 2/3(1-(1/7n))
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UP Police SI (दरोगा) Official PYP (Held On: 2 Dec 2021 Shift 1)
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Detailed Solution

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Given:

G.P. = 4/7, 4/49, 4/343, 4/2401,... up to n terms

First term (a) = 4/7

Common ratio (r) = 1/7

Number of terms = n

Formula used:

Sum of n terms of G.P., Sn = a(1 - rn) / (1 - r), where |r| < 1

Calculation:

Sn = (4/7)[1 - (1/7)n] / (1 - 1/7)

⇒ Sn = (4/7)[1 - (1/7)n] / (6/7)

⇒ Sn = (4/7 × 7/6)[1 - (1/7)n]

⇒ Sn = (2/3)[1 - (1/7)n]

∴ The correct answer is option (1).

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