1. Chapter 9 Class 11 Sequences and Series
  2. Serial order wise
  3. Ex 9.3

Ex 9.3, 7 - Chapter 9 Class 11 Sequences and Series

Last updated at May 29, 2018 by

Ex 9.3, 7 - Find sum to 20 terms in 0.15, 0.015, 0.0015 - Geometric Progression(GP): Formulae based

  1. Chapter 9 Class 11 Sequences and Series
  2. Serial order wise

    3. Ex 9.3

    Ex 9.4 →

Transcript

Ex 9.3,7 Find the sum to 20 terms in the geometric progression 0.15, 0.015, 0.0015 0.15, 0.015, 0.0015 We know that Sn = (a(1 ^ ))/(1 r) where Sn = sum of n terms of GP n is the number of terms a is the first term r is the common ratio First term a = 0.15 , Common ratio r = 0.015/0.15 ` = 15/1000 100/15 = 1/10 We know that Sum of n term = ( (1 ^ ))/(1 ) We need to find sum of 20 terms. S20 = ( (1 ^20))/(1 ) We need to find sum of 20 terms, we use the formula Sn = (a(1 ^ ))/(1 r) Putting a = 0.15, r = 0.1,n=20 S20 = (0.15(1 (0.1)20))/(1 0.1) S20 =(0.15(1 (0.1)20))/0.9 S20 = 1/6[ 1 (0.1)20] Hence, sum of 20 terms of GP is 1/6[ 1 (0.1)20]

Chapter 9 Class 11 Sequences and Series
Serial order wise

About the Author

Davneet Singh's photo - Teacher, Computer Engineer, Marketer
Davneet Singh
Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 8 years. He provides courses for Maths and Science at Teachoo. You can check his NCERT Solutions from Class 6 to 12.