Three Passengers, Two Statements Each
Three passengers on flight MN418 present together at secondary inspection. Each holds one passport - red, blue or green - and each is travelling to one of Lagos, Nairobi or Accra. Their accounts were recorded separately: P: 'Q holds the blue passport.' 'I am not travelling to Accra.' Q: 'R is travelling to Nairobi.' 'P holds the red passport.' R: 'The passenger travelling to Accra holds the green passport.' 'Q is not travelling to Lagos.' The interviewing officer notes that each passenger made exactly one true statement and one false statement. Advanced passenger information confirms that Q is not booked to Nairobi. The three checked in within four minutes on one booking, and each gave a different home address: Kano, Mombasa and Kumasi. No passenger's document shows a previous visa for the destination claimed.
1. Using the one-true/one-false rule and the API record, determine each passenger's passport colour and destination. Show the elimination, not just the answer.
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Let colours be R, G, B and destinations L, N, A.
Suppose Q is blue. P's first statement is true, so P's second must be false and P is going to Accra. Q's statements: if R were going to Nairobi, Q's second would have to be false, so P is not red. With Q blue, P and R are red/green; P not red means P green and R red. That gives Q to Lagos, and R's statements both check out: Accra is green (true), and Q is not Lagos (false). This is consistent: P green/Accra, Q blue/Lagos, R red/Nairobi.
Suppose Q is not blue. P's first statement is false, so P is not going to Accra. Q's second statement must then be true (P red), which forces Q green and R blue. Q's first statement must be false, so R is not Nairobi. R's statements: if Q went to Accra, both R1 and R2 are true, which is impossible; if Q went to Lagos, both are false; so Q must go to Nairobi and R to Accra. But the API record says Q is not going to Nairobi, so this branch fails.
Conclusion. The only solution is P green/Accra, Q blue/Lagos, R red/Nairobi.
2. What assumptions underpin the deduction, and what checks would you complete before relying on it in an interview record?
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Assumptions. The deduction depends on four things: each passenger made exactly one true and one false statement; the statements were recorded and translated accurately; the API record that Q is not going to Nairobi is correct; and colours and destinations are one-to-one.
Documentary checks. Inspect the three passports physically and compare the biodata pages; check boarding passes and baggage tags against each passenger; examine visa vignettes and entry stamps for the stated destinations; and reconcile the PNR, which should show each passenger's final sector. Ask each passenger to repeat the account separately and record the questions and answers verbatim, using an approved interpreter. Do not put the deduced answer to them in a leading way.
Use in the record. Present the deduction as a consistency test, not as proof. If the documents contradict it, the documents and physical inspection take priority, and the discrepancy itself becomes a matter for further interview. The reasoning should be recorded so a reviewer can see which branch was eliminated and why.
3. P's landing card gives his destination as Lagos. How does that affect your conclusion and what do you do next?
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In the solution P is going to Accra, so the landing card contradicts the deduction. That does not mean the puzzle should be re-solved to fit the card. There are four possibilities: the card is a clerical error; P gave a false account in the recorded statements; the API record about Q is wrong; or the one-true/one-false assumption is invalid because of mistranslation or a recording error.
The card is a self-declaration, while the solution is an inference from statements and API data, so neither automatically defeats the other. Put the discrepancy to P neutrally: 'Your landing card shows Lagos; can you explain?' Check the boarding pass, baggage tag and visa for Accra or Lagos, and ask Q and R separately without revealing the deduction. Record the answers verbatim. If the documents show Accra and the card is a slip, note and correct it through the proper amendment process. If the documents show Lagos, the original statements or the API are unreliable and the case needs further interview, not a forced answer.