If the sum of the 4th term and the 12th term of an arithmetic progression is 10, what is the sum of the first 15 terms of the progression?  Pick:  A) 65  B) 75  C) 60  D) 55  E) 50
4th term + 12th term = 10   i.e., (a+3d)+(a+11d) = 10   Now, Sum of first 15 terms = (15/2) * [2a + (15-1)d]   = (15/2) * [2a + 14d]   = (15/2) * 10 --------------- From (1)   =75   Answer : 75
<result>B</result>
If the sum of the 4th term and the 12th term of an arithmetic progression is 10, what is the sum of the first 15 terms of the progression?