Thursday, October 14, 2010

Tom's Surprise Party

This puzzle celebrates our great puzzle-solver Tom who masterfully cracked 10 different puzzles in our Family Puzzle Marathon.

Image from Flickr, distributed under CCL

Tom has been anticipating his upcoming birthday with a tremble. Do they all remember? What is my family planning to do for me? Will my old college friends show up for this big date?

He was startled when on Monday, a week before his birthday, his wife announced that they are going to have a surprise party for him one day this week.

"How it could be a surprise if I already know about this?"

Master of logical deduction, Tom started reasoning whether and when the party can take place:
"The party cannot happen on Sunday, because if it hasn't happened by Sunday,
I will know it has to happen on Sunday. Then it won't be a surprise."

"The party similarly cannot happen on Saturday, because if it has not happened by Saturday, I will know it has to happen on Saturday or Sunday. We just proved that it can't happen on Sunday, so Saturday it is. But them it can't be a surprise party."

Using the same logic Tom concluded that surprise party cannot happen on Friday, Thursday, Wednesday, Tuesday and Monday and became absolutely convinced that party is not going to take place at all. Is he right?

Submit your answer on our Family Puzzle Marathon Be first to solve three puzzles and get a prize!

This puzzle is adapted from the "Einstein's Riddle" book by J. Strangroom


Kim said...

He's wrong. He's just convinced himself that the party can't be on Wednesday, for example, so wouldn't he be surprised when everyone jumped out and yelled "SURPRISE" that day?

Wang said...

Clarifying a bit more - he is assuming things that haven't happened yet. If it happened to be Saturday and he hasn't had the party yet, then yes, it can't be on Sunday. But he's assuming that its Saturday and that no party has occurred the rest of the week. Right now, it's not Saturday and he can't assume anything.

Lynnet said...

He is correct. However, he did not think about the next week. So therefore he is also wrong.

tom said...

Last year's readers know I don't work with calculus! Tom

Maria said...

Well, Tom, you should prepare for the party.
Surprise party could happen only if you do not expected it. And as Kim correctly wrote, as soon as you (Tom) use logical deductions described in the puzzle and convince yourself that it is not going to happen and stop expecting it, it will come. Now, the question is, are we all invited? And when?

Lynnet said...

The invites are sent to the people who are invited and the the invites say when.

Anonymous said...

he is wrong. his reasoning on why it cannot happen by sunday is right. but about the rest of the days are wrong. if it hasn't happened by saturday it could happen on saturday or sunday. same with the other days.

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