[
  "Work backwards from the $15 left. Since 1/2 of the remainder was spent on the toy, the $15 left is the other 1/2 of the remainder after the watch.",
  "Remainder after watch = $15 x 2 = $30. This $30 is 3/5 of total (since 2/5 spent on watch). Total at first = $30 / 3 x 5 = $50.",
  "Answer: $50."
]