If a + 1, 2a + 1, 4a - 1 are in A.P., then the value of a is:

Answer: Option B

Let 1^st term = x = a + 1,
2^nd term = y = 2a + 1 and
3^rd term = z = 4a - 1
⇒ y - x = z - y
⇒ 2y = x + z
⇒ 2(2a + 1) = a + 1 + 4a - 1
⇒ 4a + 2 = 5a
⇒ a = 2