How many terms of G.P. 3, 32, 33, &helli | Class 11 Mathematics Chapter Sequence and Series, Sequence and Series NCERT Solutions

Q13.

How many terms of G.P. 3, 32, 33, … are needed to give the sum 120?

The given G.P. is 3, 32, 33, …

Let n terms of this G.P. be required to obtain the sum as 120.

S subscript n space equals space fraction numerator a open parentheses r to the power of n space minus space 1 close parentheses over denominator r minus 1 end fraction

Here, a = 3 and r = 3

∴ S subscript n space equals space 120 space equals space fraction numerator 3 space open parentheses 3 to the power of n space minus 1 close parentheses over denominator 3 minus 1 end fraction

rightwards double arrow 120 space equals space fraction numerator 3 open parentheses 3 to the power of n space minus 1 close parentheses over denominator 2 end fraction
rightwards double arrow fraction numerator 120 space cross times 2 over denominator 3 end fraction space equals space 3 to the power of n space minus 1
rightwards double arrow 3 to the power of n space minus 1 space equals space 80
rightwards double arrow 3 to the power of n space equals space 81
rightwards double arrow 3 to the power of n space equals space 3 to the power of 4

∴  n = 4

Thus, four terms of the given G.P. are required to obtain the sum as 120.

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Important Questions & Answers

What is the correct answer to: How many terms of G.P. 3, 32, 33, … are needed to give the sum 120??

The given G.P. is 3, 32, 33, …

Let n terms of this G.P. be required to obtain the sum as 120.



Here, a = 3 and r = 3

∴ 

∴  n = 4

Thus, f...

How do you solve How many terms of G.P. 3, 32, 33, … are needed to give the sum 120? step by step?

Step-by-step explanation:
• The given G
• P
• is 3, 32, 33, …

• Let n terms of this G

Why is this answer important for exams?

This question is important because it tests key concepts from the NCERT syllabus and is frequently asked in CBSE exams.

Which NCERT concept is used in this question?

This question is based on core NCERT concepts explained in the chapter and should be revised thoroughly before exams.

What common mistakes should be avoided in this question?

Students often lose marks by skipping steps, writing incomplete explanations, or misunderstanding keywords used in the question.

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Student Discussion

Salome
Class · · , · Jun 28, 2023
Kindly tell us what r means
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HARISH N BIDARI
Class · · , · Feb 03, 2023
Thank you sir/medam...this answer is helpful to us...😘💐🙏🙏
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HARISH N BIDARI
Class · · , · Feb 03, 2023
Thank you sir/medam...this answer is helpful to us...😘💐🙏🙏
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Riya prasad
Class · · , · Oct 30, 2021
Very good 😁😁
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Sameer sharma
Class · · , · Nov 04, 2019
Thanks for solving
the question
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