a1, a5, a13 (terms of AP) are in GP and a6 + a15 =63. Find a23
Choose the correct choice from the following:
A) 181 / 3 B) 182 / 3 C) 183 / 3 D) 184 / 3 E) 182 / 5

Rationale: a 1 a 5 = a 1 + 4 d a 13 = a 1 + 12 d now a 5 / a 1 = a 13 / a 5 - - - - > > a 1 = 4 d . . . . . . . . ( 1 ) given a 6 + a 15 = 63 - - - - > a 1 + 5 d + a 1 + 14 d = 63 - - - - > 2 a 1 + 19 d = 63 - - - - > 8 d + 19 d = 63 from ( 1 ) - - - - > d = 63 / 27 = 7 / 3 so a = 4 d = 4 * 7 / 3 = 28 / 3 from ( 1 ) a 23 = a 1 + 22 d = 28 / 3 + 22 * 7 / 3 = 182 / 3 answer : b
Answer: B