Six people, Alice, Nate, Erica, Rachael, Drew, and Chris, have witnessed a burglary and are trying to tell the police what the burglar (who got away) looked like. They disagreed quite a lot on what they’d seen. What they told the police is summarized in the figure below.
When the burglar was finally caught, each witness turned out to be wrong on 3 of the 4 characteristics, but each of the 4 characteristics had been identified correctly by at least one witness.
Can you figure out what the burglar looked like?
Solution
This problem requires relentless trial and error. We know that each person is right once and wrong three times. We could start by simply guessing at the possibilities, marking T’s and F’s in the boxes of the chart. But there’s a way to speed things up a bit, namely by noticing Erica’s and Rachael’s recollection of the clothes. One of them must be right. And since they both say 34 for age, we know 34 is wrong. So on the chart we can begin by trying Erica’s and Rachael’s lines this way:
Then we try to fill in the rest of the chart with T’s and F’s. If we arrive at an impossible situation, we change Rachael’s line (black F, blue T). If that still doesn’t work, we change Erica’s line (dark brown F and red T or brown T) – two possibilities to check out).
Eventually, the answer emerges: The robber had brown hair and blue eyes, wore a dark brown suit, and was 30 years old.
For an interesting look on training the police to be good witnesses, check VISUAL INTELLIGENCE, by Amy Herman, part 1.