Question:

A store sells four products — P, Q, R, and S — across four days (Mon–Thu), exactly one product per day.
P is not sold on Monday or Wednesday.
R is sold before Q.
S is not sold on Thursday.
Exactly one of P or Q is sold on Tuesday.
How many valid schedules are possible?

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When scheduling across days with ordering constraints, break the problem into cases based on the strongest restriction—here, the Tuesday condition on P and Q.
Updated On: Nov 30, 2025
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Correct Answer: 2

Solution and Explanation

We must assign P, Q, R, and S to Monday–Thursday, one per day, while meeting all conditions.
Step 1: Apply restrictions on P.
P is not sold on Monday or Wednesday. Therefore, P can only be on Tuesday or Thursday.
Step 2: Apply restriction on S.
S is not sold on Thursday.
Step 3: Apply the Tuesday condition.
Exactly one of P or Q is sold on Tuesday. This gives two cases: Case 1: P is on Tuesday.
Then Q is not on Tuesday. R must be before Q. S cannot be on Thursday. We check all placements under these constraints. This case produces exactly 1 valid schedule.
Case 2: Q is on Tuesday.
Then P is not on Tuesday. Since P can only go to Thursday (because Wednesday and Monday are forbidden), we assign P = Thursday. But S cannot be Thursday, so this is allowed. Now R must be before Q (Tuesday). Therefore, R must be on Monday. The only remaining product for Wednesday is S. This case also produces 1 valid schedule.
Step 4: Count valid schedules.
Each case yields exactly one valid arrangement, giving: \[ \boxed{2 \text{ valid schedules}} \] Final Answer: \(\boxed{2}\)
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