If the sum of the 4th term and the 12th term of an arithmetic progression is 30, what is the sum of the first 15 terms of the progression?  Answers.
A) 250 B) 275 C) 260 D) 225 E) 230

Rationale: 4 th term + 12 th term = 30 i . e . , ( a + 3 d ) + ( a + 11 d ) = 30 now , sum of first 15 terms = ( 15 / 2 ) * [ 2 a + ( 15 - 1 ) d ] = ( 15 / 2 ) * [ 2 a + 14 d ] = ( 15 / 2 ) * 30 - - - - - - - - - - - - - - - from ( 1 ) = 225 answer : d
Answer: D