Posted by parth on Wednesday, February 9, 2011 at 6:35am.
a = 161
a+d = 154 , so d = -7
S(m) = (m/2)(2a + (m-1)d)
0 = m/2(322 - 7m+ 7)
329m - 7m^2=0
49m - m^2 = 0
m(49-m)=0
m = 49
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