[
  "Set up: b boys, g girls originally. After: 1.10b boys, 1.04g girls. Ratio 1.10b : 1.04g = 11 : 12 gives b = 13/15 g.",
  "New pupils = 0.10b + 0.04g = 17. Substitute b = 13/15 g into this equation.",
  "Solve: (1.9/15)g = 17, so g = 2550/19 and b = 2210/19. Total = 4760/19."
]