for a given A.P. the 5th term and 12th term is 30 and 65 . find the sum of first 30 terms of A.P.
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a5 = a+4d = 30 (1)
a12 = a+11d =65 (2)
solving 1 & 2 we get
7d = 35
d = 5
a = 10
Sn = n/2 {2a+(n-1)d}
S30 = 30/2{2*10+(30-1)*5} = 2475
a12 = a+11d =65 (2)
solving 1 & 2 we get
7d = 35
d = 5
a = 10
Sn = n/2 {2a+(n-1)d}
S30 = 30/2{2*10+(30-1)*5} = 2475
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