if the sum of first 20 terms of an ap is 1/3 of sum of 20 terms and first term is 1 then find the sum of first 30 terms
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S20 =13
20/2(2a+ (20-1)d = 13
13/10= 19d+2
19d = -7/10
d = -7/190
now, S30= 30/2(2a-203/190)
= 15(2-203/190)
= 15×77/190
=. 1155/190 ans
20/2(2a+ (20-1)d = 13
13/10= 19d+2
19d = -7/10
d = -7/190
now, S30= 30/2(2a-203/190)
= 15(2-203/190)
= 15×77/190
=. 1155/190 ans
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