Question

A school schedules four classes-Math, Physics, Chemistry, and Biology-in four time slots (9 AM, 10 AM, 11 AM, 12 PM). Math is not at 9 AM. Chemistry is immediately before Physics. Biology is not at 12 PM. Which class is at 11 AM?

• A. Math
• B. Physics
• C. Chemistry
• D. Biology
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Hint:

In scheduling questions, prioritize consecutive constraints and test specific slots to satisfy all conditions systematically.

Answer 1

The Correct Option is B

- Step 1: List constraints. Four slots: 9 AM, 10 AM, 11 AM, 12 PM. Math not at 9 AM. Chemistry before Physics (consecutive). Biology not at 12 PM.
- Step 2: Assign Chemistry and Physics. Chemistry must be immediately before Physics. Possible pairs: (9,10), (10,11), (11,12).
- Step 3: Apply other constraints. Math not at 9 AM, so 9 AM is Chemistry or Biology. Biology not at 12 PM, so 12 PM is Math or Physics.
- Step 4: Test 11 AM for Physics. Try Chemistry at 10 AM, Physics at 11 AM. Slots left: 9 AM (Biology), 12 PM (Math). Check: Math not at 9 AM (satisfied), Biology not at 12 PM (satisfied), Chemistry before Physics (10,11).
- Step 5: Verify other possibilities. Chemistry at 9 AM, Physics at 10 AM: 11 AM and 12 PM for Math and Biology. Biology not at 12 PM, so 12 PM is Math, 11 AM is Biology. Valid but gives Biology at 11 AM. Chemistry at 11 AM, Physics at 12 PM: 9 AM and 10 AM for Math and Biology, but Math not at 9 AM, so 9 AM is Biology, 10 AM is Math. Valid but gives Chemistry at 11 AM.
- Step 6: Check 11 AM. Only the case with Chemistry at 10 AM, Physics at 11 AM places Physics at 11 AM.
- Step 7: Final conclusion. Option (2) Physics is the correct answer.
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