Answers

2014-01-13T16:49:42+05:30
Here there are 15 terms
so  here a=5 d=3 n=15
so Sn=n/2[2a+(n-1)d]
          =15/2[10+(15-1)3}
           =15/2 *[52]
            =780/2
            =390
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