[
  "Let total money be 9 units. Mother gets 4/9 = 4 units. Remaining = 9 - 4 = 5 units.",
  "Father gets 2/5 of 5 = 2 units. Money left = 5 - 2 = 3 units. Fraction left = 3/9 = 1/3.",
  "Benny had 1/3 of his money left. Answer: 1/3 (option A)."
]