情報検索：11月10日の見学プランを決める
Ms. Ito's third-year class at a junior high school in Fukuoka is planning a one-day visit. The school set three requirements:
(a) the group must see at least one exhibit about Hakata's history; (b) each student may spend at most ¥900 in total, including transport and admission; (c) the worksheet must be handed in on the day of the visit, which is Monday, November 10.
Transport (one way, per student)
| Method | Fare | Time | Frequency |
|---|---|---|---|
| Nishitetsu bus, Hakata → Momochi | ¥230 | 25 min | every 20 min |
| Subway + walk | ¥260 | 18 min | every 8 min |
Facilities
| Facility | Admission | Hours | Closed |
|---|---|---|---|
| Fukuoka City Museum (main) | ¥400 (high school, with ID) | 9:30–17:00 | Mondays |
| History Annex (same park) | free | 10:00–17:00 | - |
Group discount: 20% off admission for groups of 20 or more. The class has 18 students and 1 teacher. According to the school's note, the Annex holds the Hakata exhibit the worksheet asks about.
1. Which facility should the class visit, and by which transport? Show the cost per student.
Read the worked answer
Visit the History Annex, and go by bus.
Reasoning:
- Requirement (c) fixes the date at Monday, November 10, and the main museum is closed on Mondays. No price or discount can fix a closed door, so the main museum is out before money is even considered.
- The Annex is in the same park, opens daily at 10:00, is free, and holds the Hakata exhibit the worksheet needs - so requirement (a) is met.
- Cost by bus: ¥230 × 2 = ¥460 for transport, plus ¥0 admission = ¥460, which is ¥440 under the ¥900 limit.
The subway would also fit (¥520, no admission), but it spends ¥60 more to save 7 minutes on a day with no stated arrival deadline. The bus leaves more margin for a snack or a second small expense, which is the sensible choice under a hard budget.
2. A student argues: "Take the subway - it's faster, and the group discount will cover the difference." Identify what is wrong with that reasoning.
Read the worked answer
Two separate errors, and either one breaks the argument.
- The discount does not exist. The group is 18 students + 1 teacher = 19 people, and the discount starts at 20. A student who counts only the students, or who rounds 19 up to "about 20", will apply a 20% reduction that the museum will refuse at the counter.
- Even with a discount, the main museum is shut on Monday, so no price makes it usable on the planned date. Price never overrides an opening calendar.
And the arithmetic does not rescue it on another day either: subway ¥260 × 2 = ¥520, plus ¥400 admission = ¥920, over the ¥900 limit. With a genuine discount the admission would fall to ¥320 and the total to ¥840 - which is exactly why the false discount feels convincing. "Faster" and "there is a discount" are both claims to check against the table, not assumptions to build a plan on.
3. The class decides it really wants the main museum. What is the cheapest change that keeps every requirement satisfied?
Read the worked answer
Move the visit to a weekday that is not Monday (for example Tuesday, November 11) and keep the bus.
- Worksheet rule (c) says the sheet is handed in on the day of the visit, so the submission date moves with the visit. That is a permission question for Ms. Ito, not an arithmetic one - and it is the real constraint, not the fare.
- Cost on the new date by bus: ¥460 transport + ¥400 admission = ¥860, inside the ¥900 limit. ✔
- By subway it would be ¥520 + ¥400 = ¥920, over the limit, so on this plan the cheaper bus is not optional. ✔
- The 20% discount still cannot be used, because the group is 19.
Changing the date costs nothing; changing the budget or the group size is not in the students' power. So the cheapest change is the calendar, and it must be agreed with the teacher before the worksheet deadline is announced.