The first term of a GP is 27 and its 8th term is 1/81. Find the sum of its first 10 terms ?

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Airforce Group X MBT 14-Jul-2021 Shift 3
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CONCEPT:

Let us suppose a be the first term and r be the common ratio of a GP. Then the general term of a GP is given by: 

The sum of n terms of a GP with first term ‘a’ and common ratio ‘r’ is given by: 

CALCULATION:

Given: The first term of a GP is 27 and its 8th term is 1/81.

Let a be the first term and r be the common difference.

i.e a = 27

As we know that, the general term of a GP is given by: 

⇒ a8 = a ⋅ r7 = 27 ⋅ r7 = 

⇒ r = 1/3

As we know that, 

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