Bunuel wrote:
Mr. & Mrs. Smith attended an event at which there were four other married couples. At the event, various handshakes took place. No one shook hands with oneself, nor with one's spouse, and no one shook hands with the same person more than once. After all the handshakes were over, Mr. Smith asked each person, including his wife, how many hands he (or she) had shaken. To his surprise each gave a different answer. How many hands did Mrs. Smith shake?
A. 2
B. 3
C. 4
D. 5
E. 6
Are You Up For the Challenge: 700 Level QuestionsLet the couples be (A1 & A2), (B1 & B2), (C1 & C2), (D1 & D2), and (S1 & S2).
Say Mrs Smith is S1.
MAX handshakes a person can do is 8, as one cannot shake hands with oneself and one’s partner.
Total person are 10, out of which 9 have given different answers. So only possibility is when answers have been 0 to 8.
We can give any number of handshakes to other couple as we have to check for S1.
Say, A1 does handshakes with all, so 8.
What about A2?Since A1 shook hands with all except A2, all except A2 shook hand at least once. Thus A2 must have told 0.
Now, let B1 give answer 7, that is B1 shakes hands with couple C, D and S, and with A1. This means couples C, D and S had at least 2 handshakes, one with A1 and other with B1.
What about B2?None of the person in couple C, S and D would have given answer as 1, so only possibility is B2.
Similarly, Couple C would have (6,2), and couple D would have (5,3).
Only 4 as an answer is left and only person left is S1, so S1 answered 4.
C
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