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How Many Were at the Meeting (illustration)
FILE No.55Unsolved

How Many Were at the Meeting

Difficulty ★☆☆about 3 minContradictory TestimonyWhat to countNot forgetting yourself
The attendee list is lost. From four people’s handshake accounts, work out how many were there.

Case Record

The attendee list of a meeting was lost. The person in charge is trying to confirm how many people were at the venue from interviews with participants.

Only part of the interview record remains. All four statements are true, and handshake partners were limited to participants of this meeting.

Your question

How many people were at the meeting in all? Look closely at the interview record and reason it out.

Case Files

Evidence

Timeline

  1. A meeting is held and the attendee list is lost.
  2. The person in charge interviews participants.

Hints

If you get stuck, open the hints one at a time, in order.

Open hint 1

Is what remains the whole record or only part of it?

Open hint 2

From Ogawa’s point of view, how many other participants are there?

Open hint 3

Is Ogawa himself among those he shook hands with or those he did not?

Solve It

Your question

How many people were at the meeting in all? Look closely at the interview record and reason it out.

Choose the answer closest to the truth.

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The Truth

Eight

The answer is “eight.”

Ogawa shook hands with the same number as Hayashi, three, and did not shake hands with four. Counting those Ogawa shook hands with and those he did not, the participants other than Ogawa number 3 + 4 = 7. Adding Ogawa himself, there were eight participants. Just because four were interviewed does not mean there were four participants. And since no one shakes hands with himself, remember to count yourself.

Key Points

  • You do not shake hands with yourself
  • Count all “other people” from Ogawa’s view
  • Finally add Ogawa himself

Why people get fooled

You get dragged by the four interviewed or forget to count Ogawa and stop at seven.

Similar tricks

  • Making clear what is being counted
  • Not forgetting yourself

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If you view the truth, this case will not count as solved on your own. Open it anyway?

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