Question 486792: The following project uses the game of Guess Your Card. This is a game in which
each player draws (without looking) three cards. Each card has a number between 1 and 9 on it. The players then place their cards on their heads so that everyone but themselves can see the cards.
The object of the game is to guess what cards you have. The first person to do this correctly wins.
During the play, each player, in turn, draws a question at random from a stack of questions. The player then answers the question based on the cards that they see (not their own cards, which they cannot see).
An Example
* Andy has the cards 6, 6, & 7
* Belle has the cards 3, 6, & 7
* Carol has the cards 1, 1, & 9
* Dan has the cards 3, 4, & 8
Andy draws the question card, “How many 7s do you see?” He answers, “one,” because he cannot see the 7 on his own head; he sees only the 7 on Belle's head.
Next Belle draws the question card, “ Of the four even numbers, how many different even numbers do you see?” She answers, “Three,” because she sees the 4, 6, and 8 on Andy and Dan's head.
From this, Dan can conclude he has two even cards, since he can only see a 6 and Belle sees two more.
Situation
You are playing Guess Your Card with three other players. Here is what you see:
* Andy has the cards 1, 3, & 7
* Belle has the cards 3, 4, & 7
* Carol has the cards 4, 6, & 8
Andy draws the question card, “Do you see two or more players whose cards sum to the same value?” He answers, “`Yes.”
Next Belle draws the question card, “ Of the five odd numbers, how many different
odd numbers do you see?” She answers “All of them.”< /font>
Andy suddenly speaks up. "I know what I have," he says. "I have a one, a three, and a seven."
The Questions
1. What cards do you have?
In answering this question, you must write a neat and professional report. You need to briefly summarize the salient facts of the problem, explain your strategy for solving the problem, explain why your strategy will work, execute your strategy, show your mathematical working, draw conclusions from your working, and finally present your answer with a brief summery of why it is your conclusion.
2. Remember, your strategy is to use more than logic. What kind of logic will you use?
Answer by chessace(471)   (Show Source):
You can put this solution on YOUR website! Don't epect a neat professional report for free without apparant effort on your part. It's also a much too easy solve without all that strategy detail unless one is a student new to the ideas. I.e., yes YOU should.
This is an interesting problem in that the answer was available before Andy suddenly spoke.
Perhaps the posers wanted to see if that made for a variety of solutions.
The logic is "Process of elimination", with more possiblities being eliminated every time new info comes up.
After A starts, you know you have a total of 14 (B) or 18 (C).
When B sees your 5 & 9, that takes out 14, your other card is 4.
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