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NCERT Class XI Mathematics - Sequences and Series - Solutions

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Question : 41
Total: 106
0.15, 0.015, 0.0015, ... 20 terms.
Solution:  
In the given G.P.
a = 0.15, r = 0.1, n = 20
∴ Sn =
a(1−rn)
1−r
 , if |r| < 1
S20 = a
(1−r20)
1−r
 = (0.15)
(1−(0.1)20)
1−0.1
 =
(0.15)
0.9
[1−(0.1)20] =
1
6
[1−(0.1)20]
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