If the sum of the 4th term and the 12th term of an arithmetic progression is 8, what is the sum of the first 15 terms of the progression? Select the correct option.
A) 60	B) 120	C) 160	D) 240	E) 840
Let a = first term, d = common difference.   4th term = a+3d   12th term = a+11d   a+3d + a+11d = 8   2a + 14d = 8   a + 7d = 4.   Sum of the first 15 terms = 15/2 (2a + 14d) = 15 (a+7d) = 15 (4) = 60. 60ns (60)
<result>A</result>
If the sum of the 4th term and the 12th term of an arithmetic progression is 8, what is the sum of the first 15 terms of the progression?