[
  "Add the fractions spent on Day 1 and Day 2. Find what fraction remains. Then divide by 1/10 (the daily rate from Day 3) to find how many days.",
  "Spent by end of Day 2: 1/5 + 1/4 = 4/20 + 5/20 = 9/20. Remaining: 11/20. From Day 3, uses 1/10 = 2/20 per day. 11/20 / 2/20 = 11/2 = 5.5 days.",
  "Day 3-7 (5 full days) uses 10/20, total spent = 19/20. Day 8 uses the last 1/20. Answer: Day 8."
]