1. If the sum of the first 11 terms of an arithmetic progression equals that of the first 19 terms, then what is the sum of the first 30 terms?





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  • By: anil on 05 May 2019 02.30 am
    Sum of the first 11 terms = 11/2 ( 2a+10d)  Sum of the first 19 terms = 19/2 (2a+18d)  => 22a+110d = 38a+342d => 16a = -232d => 2a = -232/8 d = -29d Sum of the first 30 terms = 15(2a+29d) = 0
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