The 3 cabins together hold 3 × the average. Let cabin 3 be 1 unit: cabin 1 = 1 unit + 50, cabin 2 = 2 units.

Cabin 31Cabin 1150Cabin 211total = 3 × 190 = 570

Plain numbers are given; italic underlined numbers are worked out.

  1. Total → 3 × 190 = 570
  2. 1 + 1 + 2 = 4 units, plus 50 → 570
  3. 4 units → 570 − 50 = 520
  4. 1 unit (cabin 3) → 520 ÷ 4 = 130
  5. Cabin 2 → 2 × 130 = 260

There are 260 passengers in the second cabin.

Check: 130 (3rd) + 180 (1st) + 260 (2nd) = 570; 570 ÷ 3 = 190. ✓