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

Last updated at May 29, 2018 by Teachoo

Last updated at May 29, 2018 by Teachoo

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]

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Chapter 9 Class 11 Sequences and Series

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Davneet Singh

Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 9 years. He provides courses for Maths and Science at Teachoo.