IBPS SO Prelims Exam Model Paper 8

Let the three numbers are a, a + d and a + 2d, where d is the common difference.
⇒ a ∶ (a + 2d) = 1 ∶ 3
⇒ 3a = a + 2d
⇒ 2a = 2d
⇒ a = d
Now the second number is 1000
⇒ a + d = 1000
⇒ a + a = 1000
⇒ 2a = 1000
⇒ a = 500
∴ The first number is 500