<PRE><B>Question 1003399</B>
{{{ S[n]}}} the sum of n terms of an AP is 


{{{S[n] = (n/2)(2a + (n-1)d)}}}



{{{t[3] = a+2d}}}}

d=3.5

24 = a+ 2*3.5

24 = a +7

a=17

a= 17 d= 3.5

{{{S[n] = (n/2)(2a + (n-1)d)}}}

{{{S[25] = (25/2)(2*17 + (25-1)3.5)}}}


= 12.5 (34+84)

=12.5 *128

=1600

Sum of 25 terms is 1600







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