Q. 634.0( 4 Votes )

Sum of the first

Answer :

Here, first term = a = 10

Let the Common difference = d


Sum of first 14 terms = S14 = 1505


Now, Sum of n terms of this arithmetic series is given by:


Sn = [2a + (n - 1)d]


S14 = [2(10) + (14 - 1)d] = 1505


7 × [20 + 13d] = 1505


[20 + 13d] = 215


13d = 195


d = 15


Now, nth term is given by:


an = a + (n - 1)d


a25 = 10 + (25 - 1)15


= 10 + (24 × 15)


= 10 + 360


= 370

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