Hari (H), Gita (G), Irfan (I) and Saira (S) are siblings (i.e. brothers and…

Answer: SGHI

Explanation:

• Each successive sibling is less than 3 years younger, so each adjacent age gap is either 1 or 2 years. Because Gita and Saira differ by exactly 1 year, they must be adjacent in the birth order.

• Gita is not the oldest and Saira is not the youngest. Therefore the adjacent Gita–Saira pair can appear only in these placements: S G _ _, _ G S _, or _ _ S G.

• Model the four ages as positions 1..4 with ages: x, x - a, x - a - b, x - a - b - c where a, b, c are each 1 or 2 (the successive gaps).

• Check each feasible adjacency placement:

  • S G H I (positions 1,2,3,4 = S,G,H,I): the inequality H + G > I + S becomes (x - a - b) + (x - a) > (x - a - b - c) + x, which simplifies to a < c. Since Gita and Saira differ by 1 year, a = 1, so we need c = 2. This is achievable. Example: choose gaps a = 1, b = 1, c = 2 and x = 10, giving ages S = 10, G = 9, H = 8, I = 6; then H + G = 17 > I + S = 16.

  • I G S H (positions 1,2,3,4 = I,G,S,H): adjacency forces b = 1. The inequality H + G > I + S reduces to -(a + c) > 0, which is impossible because a and c are at least 1. So no allowed gaps can satisfy the inequality here.

  • I H S G (positions 1,2,3,4 = I,H,S,G): adjacency forces c = 1. The inequality again reduces to -(a + c) > 0, impossible for a, c ≥ 1, so this ordering cannot work.

  • H S I G places Gita and Saira non-adjacent, contradicting the given 1-year difference, so it is invalid.

• Therefore the only ordering consistent with all constraints is S G H I.